Plasma generating device and surface processing device and method for processing wafers in a uniform magnetic field

ABSTRACT

A surface processing device and method for forming a magnetic field having a uniform strength over a wide area of an electrode surface to generate a uniform high density plasma over the overall surface of a wafer. The device comprises a vacuum container contains a first electrode and a second electrode disposed opposite to the first electrode; a gas feeding system for feeding a predetermined gas into the vacuum container; an evacuating system for maintaining the inside of the container at a reduced pressure; an electric field generating system for generating an electric field in a region between the first and second electrodes; and a magnetic field generating system for generating a magnetic field in the vacuum container. The magnetic field generating system comprising a plurality of magnets arranged around the outer periphery of the container so as to form a ring in such a manner that directions of magnetization thereof differ from adjacent magnetic element making a 720 degree rotation along the circumference of said ring.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to plasma generating devices, and surfaceprocessing devices and methods, and more particularly to surfaceprocessing device and method used for etching and forming thin films onthe basis of a vapor phase growth method.

2. Description of the Related Art

Conventionally, there has been reactive ion etching (RIE) as one of dryetching methods widely used for fine working in a semiconductor devicemanufacturing process. Further, there has been a magnetron RIE in whicha magnetic field is applied to plasma generated in the RIE process so asto increase the density of the plasma, the etching rate and henceimprove the accuracy of the fine working.

FIG. 57 illustrates an example of the conventional devices used forcarrying out the magnetron RIE. The device is provided with an anode 7attached to an upper inner wall of a vacuum container 1, and a cathode 2disposed opposite to the first electrode and also functioning as asupport for a substrate 3. Electric power generated at a high frequencysource 5 is applied across the anode 7 and cathode 2 through a matchingcircuit 14. The resulting electric field generates a plasma in a regionbetween these electrodes. By a self-biasing electric field induced onthe surface of the cathode 2, reactive ions in the plasma areaccelerated to cause the ions to impinge on a wafer to thereby advancean etching reaction. In the magnetron RIE, a magnetic field generated bya magnet 10 is applied to the self-biasing electric field in a directionperpendicular to the direction of the electric field. In FIG. 57, linesof magnetic force 11 are schematically shown. By intersecting theelectric field E with the magnetic field B at the right angle, theelectrons in the plasma are drifted by Lorentz force in the direction ofE×B, which causes the electrons to run in the plasma over a longdistance. As a result, the frequency of the electrons to impinge onneutral molecules and atoms increases and hence the plasma densityincreases. Further, by applying the magnetic field to the plasma, theelectrons are confined to within the plasma to prolong their lifetime(the period of time taken until the electrons finally impinge on thechamber sidewall, electrode and wafer) and hence the plasma density isincreased.

When the plasma density is increased, not only the etching rate isincreased, but also the directivity of the ions is increased, and theion energy which would increase damage and decrease the etch selectivityis maintained sufficiently low even when the gas pressure is reduced tosuppress the reaction of neutral species and a film to be etched(isotropic reaction).

As described above, the magnetron RIE device exhibits excellentperformances. Therefore, it has been used in the processing of variousthin films. However, with the magnet used in the conventional manner,the uniformity of the etching rate is degraded because of unevenness ofthe strength and direction of the magnetic field generated by themagnet. Further, ions are disturbed in directivity so that they enterthe wafer surface at oblique angles. As a result, a desirableanisotropic etching cannot be performed and the rate of etching to apattern having a narrow width or a high aspect ratio is decreased.

For example, as shown in FIG. 58, by the etching device of FIG. 57, thewafer 3 has a satisfactory etched shape at the central portion B whilethe peripheral portions A, C of the wafer are obliquely etched due tooblique incident direction of the ions to thereby have undesirableanisotropic oblique configuration.

Although the mechanism causing such undesirable etched configuration hasnot been known in a strict sense, it can be explained as follows.

Referring to FIG. 59, the lines of magnetic force formed in theperipheral portion of the wafer 3 are not parallel to the surface of thewafer, but are curved and formed obliquely relative to the wafer. Sincethe electric field is relatively weak in the plasma compared with themagnetic field, the electrons are influenced solely by the magneticfield and move with a spiral motion having a radius of about 1 mm whilesurrounding the lines of magnetic force. Therefore, at a place where thelines of magnetic force intersect with the wafer 3, electrons enterobliquely into the wafer along the lines of magnetic force. Since themass of ions directly involving the etching reaction is large, themoving direction of the ions is not greatly bent by the magnetic field.However, when electrons enter obliquely into grooves in the wafer underetching, they impinge on only one side of the groove walls. As a result,the quantities of the electric charges on both sides of the groove wallsare not equal. Thus, another electric field occurs across both sides ofthe groove walls, which acts on the ions to bend its moving direction sothat undesirable etched shape is produced.

It is known that when a substrate on which devices having a MOSstructure are formed is processed, such uneven distribution of electriccharges on the wafer surface would cause insulation break down through athin insulating film such as a gate oxide film or increase in theleakage current.

Since the etching device of FIG. 57 uses a leakage flux of the magneticfield, a magnet producing a very large magnetic field must be used toobtain a required magnetic field on a substrate to be processed.However, a magnet producing a large magnetic field has a very largeweight so that it is very difficult to assemble the etching device. Eachtime the material of a substrate to be processed is changed, the magnetmust be changed so as to change the distribution and strength of themagnetic field on the substrate. A large magnetic field produced by themagnet influences on broad regions surrounding the etching device.Therefore, electronic devices sensitive to magnetism cannot be used inthe surrounding broad regions. There is a multi-chamber system in whicha device has a plurality of reactive chambers each having a magnet. Inthe multi-chamber system, leakage flux from the plurality of reactivechambers interfere with each other to distort each magnetic field in thereactive chamber, which influence the process greatly. Therefore, theconventional device utilizing the leakage flux of the magnet cannot beused in the multi-chamber system.

A device has been proposed which is provided with two coils ofelectromagnets at the opposing sides of a vacuum processing chamber.These two coils are disposed perpendicular to each other and suppliedwith alternating currents whose phases are shifted by 90 degrees so thatthe magnetic field produced by the electromagnets rotates. As themagnetic field rotates, however, the strength and distribution of themagnetic flux are changed so that the magnetic field is distorted.Further, as the frequency of the alternating current applied to thecoils is increased to increase the rotation speed of the magnetic field,the impedance of the coils increases. Thus, there is a limit to therotational speed. In order to supply a uniform magnetic field to theoverall surface of the wafer, the coil diameter is required to besufficiently large compared to the distance between the coils or thesize of the container of the device. As the diameter of the waferincreases, the size of the coil must be increased so that the currentflowing through the coils and the size of a Dower source thereforincrease.

Furthermore, since the strong magnetic field acts on regions in which nomagnetic field is required inside and outside of the container,electro-mechanical parts sensitive to magnetism cannot be disposed inthose regions. Further, magnetic shielding for protecting outsidedevices is required.

The above problems occur not only in the etching process, but also inall surface processing which use plasma such as depositing processesincluding sputtering and CVD, impurity implantation processes andsurface modifying precesses, in terms of uniformity, accuracy, anddamage.

As described above, since the strength and direction of the magneticfield are uneven in the conventional magnetron RIE device, uniformetching is not maintained, and the directivity of ions is disturbed, sothat ions enter obliquely into a substrate surface to be processed tothereby render high anisotropic etching difficult. When the magneticfield strength is tried to be increased, the magnet weight is larger andthe device becomes difficult to compose. Each time the distribution andstrength of the magnetic field is changed, the magnet used must bechanged. In addition, leakage magnetic field is large and a plurality ofreactive chambers cannot be provided in close relationship.

SUMMARY OF THE INVENTION

The present invention is made in view of the above problems. It is anobject of the present invention to provide a surface processing deviceand a method of forming a magnetic field of uniform strength over a widerange of an electrode surface to maintain a uniform high-density plasmaover the overall surface of a wafer.

In the first aspect of the present invention, there is provided a plasmagenerating device comprising a vacuum container provided with a firstelectrode and a second electrode disposed opposite to the firstelectrode; gas feeding means for feeding a predetermined gas into thevacuum container; evacuating means for maintaining the inside of thecontainer at a reduced pressure; electric field generating means forgenerating an electric field in a region between the first and secondelectrodes; and magnetic field generating means for generating amagnetic field in the vacuum container, the magnetic field generatingmeans comprising a plurality of magnet elements arranged around theouter periphery of the container so as to form a ring in such a mannerthat directions of magnetization thereof differ from adjacent magneticelement by a predetermined phase making a 360 degree rotation along halfthe circumference of the ring, whereby a plasma is generated.

in the second aspect of the present invention, there is provided asurface processing device comprising a vacuum container provided with afirst electrode and a second electrode disposed opposite to the firstelectrode for supporting thereon a substrate to be processed; gasfeeding means for feeding a predetermined gas into the vacuum container;evacuating means for maintaining the inside of the container at areduced pressure; electric field generating means for generating anelectric field in a region between the first and second electrodes; andmagnetic field generating means for generating a magnetic field in thevacuum container, the magnetic field generating means comprising aplurality of magnets arranged so as to form a ring in such a manner thatmagnetized direction of each magnetic element differs from adjacentmagnetic element by a predetermined angle making a 360 degree rotationalong half the circumference of the ring.

Preferably, the surface processing device further comprises means forrotating the magnetic field generating means around a central axisthereof relative to the substrate to be processed.

Preferably, the surface processing device further comprises magneticfield strength controlling means for adjusting the magnetic fieldstrength within the container by changing the direction of magnetizationof at least one of the magnets.

Preferably, the surface processing device further comprises means formoving the magnetic field generating means vertically.

Preferably, the magnetic field generating means comprises at least twoseparate magnetic field generating sub-means disposed vertically witheach other having the same central axis, at least one of the magneticfield generating sub-means being movable vertically.

Preferably, the magnetic field generating means comprises at least twoseparate magnetic field generating sub-means disposed vertically witheach other such that distance between the two magnetic field generatingsub-means is adjustable.

Preferably, the magnetic field generating means comprises at least twoseparate magnetic field generating sub-means disposed vertically witheach other such that the difference in phase between the two magneticfield generating sub-means is adjustable.

Preferably, the plurality of magnet elements are disposed withdirections of magnetization thereof being shifted by a predeterminedphase with adjacent magnet element, and comprising means for rotatingeach of the plurality of magnet elements.

In the third aspect of the present invention, there is provided asurface processing device comprising a vacuum container provided with aplurality of reactive chambers; a first electrode provided in at leastone of the reactive chambers; a second electrode provided opposite tothe first electrode; gas feeding means for feeding a predetermined gasinto the at least one of reactive chambers; evacuating means formaintaining the inside of the at least one of reactive chambers at areduced pressure; electric field generating means for generating anelectric field in a region between the first and second electrodes; andmagnetic field generating means for generating a magnetic field in theat least one of reactive chambers, the magnetic field generating meanscomprising a plurality of magnet elements arranged around the outerperiphery of the at least one of reactive chambers so as to form a ringin such a manner that directions of magnetization thereof differ fromadjacent magnetic element by a predetermined phase making a 360 degreerotation along half the circumference of the ring.

In the fourth aspect of the present invention, there is provided asurface processing method comprising the steps of feeding apredetermined gas into a vacuum container provided with a firstelectrode and a second electrode disposed opposite to the firstelectrode; placing a substrate to be processed on the second electrode;generating an electric field in a region between the first and secondelectrodes; and forming a uni-directional magnetic field substantiallyparallel to a surface of the substrate to be processed by means of aplurality of magnet elements arranged so as to form a ring in such amanner that directions of magnetization thereof differ from adjacentmagnetic element by a predetermined phase making a 360 degree rotationalong half the circumference of the ring, thereby to induce a plasmawithin the vacuum container to process the surface of the substrate.

In the fifth aspect of the present invention, there is provided asurface processing device comprising a vacuum container provided with afirst electrode and a second electrode disposed opposite to the firstelectrode, the second electrode supporting thereon a substrate to beprocessed; gas feeding means for feeding a predetermined gas into thevacuum container; evacuating means for maintaining the inside of thecontainer at a reduced pressure; electric field generating means forgenerating an electric field in a region between the first and secondelectrodes; and magnetic field generating means for generating amagnetic field in the region between the first and second electrodes,the magnetic field generating means comprising a plurality of magnetelements arranged so as to form a ring around the vacuum container insuch a manner that directions of magnetization thereof differ fromadjacent magnetic element by a predetermined phase making a 360 degreerotation along half the circumference of the ring; and electrodeposition setting means for moving the second electrode to change thedistance between the first and second electrodes within a syntheticmagnetic field generated by the plurality of magnet elements.

In the sixth aspect of the present invention, there is provided asurface processing device comprising a vacuum container provided with afirst electrode and a second electrode disposed opposite to the firstelectrode, the second electrode supporting thereon a substrate to beprocessed; gas feeding means for feeding a predetermined gas into thevacuum container; evacuating means for maintaining the inside of thecontainer at a reduced pressure; electric field generating means forgenerating an electric field in a region between the first and secondelectrodes; magnetic field generating means for generating a magneticfield in the region between the first and second electrodes, themagnetic field generating means comprising a plurality of magnetelements arranged so as to form a ring in such a manner that directionsof magnetization thereof differ from adjacent magnetic element by apredetermined phase making a 360 degree rotation along half thecircumference of the ring; and diameter changing means for changing thediameter of the ring formed by the plurality of magnet elements.

Preferably, the surface processing device further comprises means forrotating the magnetic field generating means around a central axisthereof relative to the substrate to be processed.

Preferably, the magnetic field generating means comprises at least twoseparate magnetic field generating sub-means disposed vertically witheach other having the same central axis, at least one of the magneticfield generating sub-means being movable vertically.

Preferably, the magnetic field generating means comprises at least twoseparate magnetic field generating sub-means disposed vertically witheach other having the same central axis such that distance between thetwo magnetic field generating sub-means is adjustable.

Preferably, the magnetic field generating means comprises at least twoseparate magnetic field generating sub-means disposed vertically witheach other having the same axis such that the difference in phasebetween the two magnetic field generating sub-means is adjustable.

Preferably, the magnetic field generating means comprises at least twoseparate magnetic field generating sub-means disposed vertically witheach other having the same axis and the directions of magnetic fieldsgenerated by the two magnetic field generating sub-means are changed tochange the strength of the synthetic magnetic field.

Preferably, the plurality of magnet elements are disposed withdirections of magnetization thereof being shifted by a predeterminedphase with adjacent magnet element, and comprising means for rotatingeach of the plurality of magnet elements.

In the seventh aspect of the present invention, there is provided asurface processing device comprising: a vacuum container provided with afirst electrode and a second electrode disposed opposite to the firstelectrode, the second electrode supporting thereon a substrate to beprocessed; gas feeding means for feeding a predetermined gas into thevacuum container; evacuating means for maintaining the inside of thecontainer at a reduced pressure; electric field generating means forgenerating an electric field in a region between the first and secondelectrodes; and magnetic field generating means for generating amagnetic field in a region between the first and second electrodes, themagnetic field generating means comprising a plurality of magnetsarranged so as to form a ring in such a manner that directions ofmagnetization thereof differ from adjacent magnetic element by apredetermined phase making a 360 degree rotation along half thecircumference of the ring, at least one pair of opposing magnet elementshaving direction of magnetization extending toward the central axis ofthe ring, the pair of magnetic elements having a magnetic strength equalto each other with directions thereof opposite to each other.

In the eighth aspect of the present invention, there is provided asurface processing device comprising a vacuum container provided with afirst electrode and a second electrode disposed opposite to the firstelectrode, the second electrode supporting thereon a substrate to beprocessed; gas feeding means for feeding a predetermined gas into thevacuum container; evacuating means for maintaining the inside of thecontainer at a reduced pressure; electric field generating means forgenerating an electric field in a region between the first and secondelectrodes; magnetic field generating means for generating a magneticfield in the region between the first and second electrodes, themagnetic field generating means comprising a plurality of magnetsarranged around the vacuum container so as to form a ring in such amanner that directions of magnetization thereof differ from adjacentmagnetic element by a predetermined phase making a 360 degree rotationalong half the circumference of the ring; and a dividing member providedaround periphery of the substrate to be processed in radius direction ofthe ring, for dividing a space in the vacuum container into two regions,one region containing the substrate to be processed, another region notcontaining the substrate to be processed.

According to the first aspect of the present invention, a high densityplasma can be generated.

According to the second aspect of the invention, a plurality of magnetsarranged so as to form a ring in such a manner that directions ofmagnetization thereof differ from adjacent magnetic element by apredetermined phase making a 360 degree rotation along half thecircumference of the ring thereby to form a uni-directional magneticfield substantially parallel to the surface of the first electrode.Thus, a significantly uniform magnetic field is formed, the plasmapotential and the self bias are equalized, and high anisotropic uniformetching is achieved. Damage due to the etched substrate surface beingcharged up is low. The first electrode may be formed as a part of theupper wall of the vacuum container or disposed within the container.

According to the conventional device, since the generated magnetic fieldhas a curved magnetic flux, a uniform plasma field cannot be formed evenby rotating the magnetic field. In contrast, according to the secondaspect of the present invention, the generated magnetic field has acomplete parallel magnetic flux, a completely uniform processing byrotation of the magnetic field.

Further, a very high magnetic field strength (of up to several kG) isobtained while maintaining its uniformity compared to the conventionaldevice. Thus, the ion energy and damage are reduced even in a high speedprocess.

Furthermore, since the weight of the magnet elements are relativelysmall, the associated peripheral mechanisms and hence the overall devicecan be light and reduced in size.

Since the magnet is of an internal magnetic field type which gives asmall amount of leaking magnetic flux to outside, there is littleadverse influence on other devices. Thus, even in a multi-chamber typedevice having a plurality of reactive chambers, processing in onechamber does not influence on processing of other chambers.

Unlike the conventional device, no magnet is provided over the anodeside. Therefore, a space on the anode side can be provide with otherdevices such as a monitor for monitoring plasma in the vacuum chamberand the surface state of a substrate to be processed or an upperevacuating mechanism disposed opposing to the wafer. Further, it isconvenient to supply a high frequency Dower to the anode side.

The magnetic field generating means may be rotated to provide a furtheruniform magnetic field. It can be rotated freely without any limit as inan electromagnet coils. Since the magnetic field generating means has aconcentric rotationally symmetric structure, a high speed rotation canbe possible with a simple structure compared with the conventionaldevice.

The strength of the magnetic field can be adjusted by changing thedirection of magnetization of at least one of the magnet elements of themagnetic field generating means without any magnet element beingreplaced with another.

Either the magnetic field generating means or the electrode on which thesubstrate is placed may be constructed such as to vertically movable sothat conveying the substrate into/out of the container is facilitated.

The magnetic field generating means may have a slit at an appropriateheight a slit through which the substrate to be processed is conveyedinto/out of the container. Various experiments show that such slit doesnot influence on the direction of the magnetic field and therefore the aparallel magnetic flux can be obtained.

The magnetic field generating means may comprise at least two separatemagnetic field generating sub-means disposed vertically having the samecentral axis, at least one of the magnetic field generating sub-meansbeing movable vertically to facilitate the conveyance of the substrateinto/out of the container.

The magnetic field generating means may comprise at least two verticallydisposed magnetic field generating sub-means having the same centralaxis with the distance between the magnetic field generating sub-meansbeing adjustable. With this structure, the strength of the magneticfield can easily adjusted without exchanging the magnet elements withother ones.

The magnetic field generating means may comprise at least two separatemagnetic field generating sub-means disposed vertically with the samecentral axis. By adjusting the phase difference between these twomagnetic field generating sub-means, the strength of the magnetic fieldcan easily be adjusted without changing the magnet elements.

The magnetic field generating means may comprise at least two separatemagnetic field generating sub-means disposed vertically with the samecentral axis. By rotating these two magnetic field generating sub-meansin opposite directions, the strength of the magnetic field can easily beadjusted without changing the magnet elements.

The magnet elements constituting the magnetic field generating means maybe rotated individually while they are arranged with their directions ofmagnetization being shifted by a predetermined phase thereby to form amagnetic field equivalent to that obtained when the overall magnet ringis rotated.

According to the third aspect of the invention, since very littlemagnetic flux is leaked, surface processing operations can be performedsimultaneously in the plasma generated in each of a plurality ofreaction containers without being influenced by each other.

According to the fourth aspect of the present invention, auni-directional magnetic field is generated substantially parallel tothe surface of the second electrode. Since etching is performed byactive seeds produced by the plasma generated on the substrate surface,the etching rate and the shape of etched portion are improved, andelectrostatic damage such as the break down of gates due to thedistribution of the plasma density is reduced. In addition, a strongmagnetic field in the order of kG increases the density of the magnetronplasma and decreases the ion energy.

The present invention is especially effective for the surface processingof a substrate to be processed in which electric devices are formedthereon, that is, especially effective for establishment of auni-directional magnetic field substantially parallel to the surface ofthe second electrode, and for production of active species using theplasma induced over the substrate. Although the substrate is exposed tothe plasma and hence electrically charged, no high voltage is appliedacross the thickness of the thin insulating film as long as theelectrical charging is uniform in the surface of the substrate, and nogate break down occurs. Thus, stable thin film formation and etchingexcellent in directivity are achieved.

In the substrate processing device using a dipole ring magnetconstructed by a plurality of magnet elements arranged in the form of aring as is described later, uniformity is maintained such that thedifference in magnetic field strength between the central and peripheralportions of the substrate to be processed can be maintained less than20%, and that the tilt in the XY plane is within 5 degrees. Although thedipole ring magnet generates an excellent magnetic field, when suchmagnet is used in a magnetron RIE device under a low pressure of 5 mTorrwhich is considerably lower than the pressure usually used in etchingprocess wi magnetron RIE's, the etching rate may be decreased in theperiphery of the substrate. Further, when a substrate formed withelements of a MOB structure is processed by the magnetron RIE device,insulation break down in a thin oxide film such as the gate oxide filmis likely to occur.

FIGS. 60 and 61 show the intra-surface distributions of the etchingrates of oxide films by the conventional magnetron RIE device using theconventional magnet and the dipole ring magnets, respectively in whichthe magnets are rotated. In these drawings, N and S denote thedirections of the magnetic poles and E an W denote the east and westdirections with respect to the magnets. Although the causes of areduction in the etching rates in the peripheral portions of thesubstrate to be processed are not known, it may be understood asfollows.

As shown by curve a in FIG. 22, (curve b denotes a distribution ofmagnetic field strength formed by the conventional magnet), thedistribution of magnetic field strength formed by the dipole ring magnetis uniform over the substrate area or over an area larger than thesubstrate area. However, the magnetic field strength is rapidly reducedin the vicinity of the magnet. Thus, although the magnetic fielddistribution is uniform through substantially the overall surface of thesubstrate compared to the conventional magnetron RIE even under a lowpressure of 5 mTorr which is considerably lower than the pressureusually used in etching process, a rapid reduction in the etching rateoccurs in the periphery of the substrate. The reason for this ispossibly that since the magnetic field strength is uniform, there isalmost no mirror effect which generate a mirror magnetic field.Therefore, in the peripheral portion of the substrate, electron arelikely to get loose and the density of the plasma is reduced. When asubstrate is exposed to the plasma, the substrate is electricallycharged. If there is a difference in the plasma density varies indensity, the surface of the substrate is unevenly charged so that a highvoltage is applied across the thickness at a portion of the thininsulating film. Thus, insulation break down occurs at this portion.

The dipole ring magnet may comprises an upper and a lower dipole ringbetween which a load lock carrying system is provided to convey thesubstrate from the load chamber to the etching chamber and vice versa.There is provided a mechanism for moving each ring up and down, thespace between the upper and the lower rings becoming wider and narrower.However, the spacing between the rings cannot be narrower than theheight of the carrying system. Because of the space between the rings,the strength of the magnetic field at a peripheral area is weakenedalthough a uniform magnetic field parallel to the surface of thesubstrate is generated. The reduction in the magnetic field in theperipheral region can be compensated for by adding an auxiliary magneticfield to the peripheral region, especially in the vicinity of the N andS poles, and by rotating slightly the direction of magnetization of themagnet elements in the vicinity of the N and S poles toward thedirection of magnetization of the dipole ring magnet. With thisarrangement, a uniform parallel electric field can be generated in thevacuum container to thereby confine the plasma therein so that it ispossible to perform surface processing such as etching with little iondamage, stable film formation, and satisfactory directivity. However, adevice structure becomes complicated in the actual mass productionprocess.

According to the fifth aspect of the present invention, simplificationof the device structure and uniform processing are intended. A substrateto be processed is conveyed into a magnetic field generated by magneticfield generating means by moving the substrate vertically. Therefore, itis not necessary to divide the magnetic field generating means. As aresult, there occurs no reduction in the magnetic field at a peripheralregion and there is no need to add an auxiliary magnetic field toprevent such reduction. Thus, a device structure becomes simple with auniform high density magnetic field and equalized plasma potential andself bias voltage over the overall surface of the wafer. With thedevice, highly anisotropic uniform surface processing is achieved on thesurface of a substrate.

Further, the height of the cathode electrode (second electrode) on whicha substrate to be processed is placed may be set at any position. Thedistance between the electrodes is changeable to an optimal one duringplasma processing depending on the substrate material, gas and pressureto thereby change the processing characteristic.

According to the sixth aspect of the present invention, the diameter ofthe ring and hence the magnetic field strength generated within the ringare changed to control the ion energy to change the processingcharacteristic.

Therefore, for example, each time the optimal magnetic strength variesdepending on the substrate material or the gas in the surface processingof the substrate, no magnet elements having the optimal magneticstrength are required to be changed. When sequential processing can bemade efficiently under the optimal magnetic field.

According to the seventh aspect of the present invention, the magneticfield generating means comprises a plurality of magnet elements arrangedso as to form a ring along half the circumference of which the directionof magnetization of the magnet elements makes a complete rotation as awhole, at least one pair of opposite ones of the magnet elements hascomponents perpendicular to the ring and axially symmetrical around thecentral axis of the ring. Thus, the height of the space for a magneticfield parallel to a surface of the substrate may be deviated from themidheight of the magnetic field generating means.

Preferably, the space for a parallel magnetic field is formed at anyheight within the ring by changing the magnitude of directionalcomponents axially symmetrical to each other and perpendicular to thering.

Thus, when the substrate is processed by a plasma within the parallelmagnetic field, the substrate is not required to be carried to thevicinity of the center of the magnet which is the parallel magneticfield space formed by the dipole ring magnet, the distance of movementof the lower electrode is reduced, and the moving mechanism issimplified.

The magnitude of the vertical components can easily be changed to changethe magnetic field strength during processing.

In order to change the magnetic field strength during the processing,the magnitude of its vertical components is easily changed.

According to the eighth aspect of the present invention, it is possibleto Generate a magnetized plasma only in a region in which a substrate tobe processed is disposed and the substrate in that region is notinfluenced by magnetized plasma Generated by other devices.

it is a further object of the present invention to provide a substrateprocessing device which forms a uniform plasma over a wide range of theelectrode surface, confines the plasma and maintains the plasma at highdensity over the overall surface of the wafer.

Accordingly, in the ninth aspect of the present invention, there isprovided a surface processing device comprising a vacuum containerprovided with a first electrode and a second electrode disposed oppositeto the first electrode, the second electrode supporting thereon asubstrate to be processed; gas feeding means for feeding a predeterminedgas into the vacuum container: evacuating means for maintaining theinside of the container at a reduced pressure; electric field generatingmeans for generating an electric field in a region between the first andsecond electrodes; and magnetic field generating means for generating amagnetic field in the vacuum container, the magnetic field generatingmeans comprising a plurality of magnets arranged around the vacuumcontainer so as to form a ring in such a manner that directions ofmagnetization thereof differ from adjacent magnetic element by apredetermined phase making a 360 degree rotation along half thecircumference of the ring, the strength of the magnetic field in thevicinity of the peripheral portions of the ring in its north-south (N-S)pole direction being equal to, or greater than, that of the magneticfield at the center of the ring.

The magnetic field strengths in the peripheral portions of the ring inits N-S direction are equal, or stronger than, that in the center of thering to exert a force to push the plasma back from the peripheralportions of the ring toward its center to thereby confine the plasmabetween the first and second electrodes. The first electrode mayconstitute a part of a wall of the container insulated electrically fromthe remaining portion of the container or may be provided separatelywithin the container. For example, first magnetic field generating,means which comprises a plurality of magnets disposed so as to form aring along half the circumference of which the direction ofmagnetization of the magnet elements makes a complete rotation as awhole, generates a uni-directional magnetic field substantially parallelto a surface of the first electrode. Second magnetic field generatingmeans may be provided so as to generate a mirror magnetic field to thevicinity of the substrate in a plasma magnetic field expanding uniformlyto generate a high density plasma to thereby equalize the plasmapotential and self bias voltage to perform highly anisotropic uniformhigh speed surface processing on the surface of the substrate.

Preferably, at least one second magnet is disposed within the magneticfield generated by a first magnet ring composed of magnet elementsdisposed so as to form a ring along half the circumference of which thedirection of magnetization of the magnet elements makes a completerotation as a whole such that the magnetic field in the peripheralportions of the ring in its N-S direction is equal to, or stronger than,that at the center of the ring to thereby confine the plasma inducedbetween the first and second electrodes within this space.

Preferably, the magnetic field generating means comprises a plurality ofmagnet elements arranged so as to form a ring along half thecircumference of which the direction of magnetization of the magnetelements makes a complete rotation as a whole. The plurality of magnetelements produces magnetic fields having different strengths such thatthe synthetic magnetic field in the vicinity of the ring periphery inits N-S direction being equal to, or greater than, that of the magneticfield at the center of the ring to thereby confine the plasma inducedbetween the first and second electrodes within this space.

Preferably, the magnetic field generating means comprises a plurality ofmagnet elements arranged so as to form a ring along half thecircumference of which the direction of magnetization of the magnetelements makes a complete rotation as a whole. The plurality of magnetelements produces magnetic fields having different directions ofmagnetization such that the synthetic magnetic field in the vicinity ofthe ring periphery in its N-S direction being equal to, or greater than,that of the magnetic field at the center of the ring to thereby confinethe plasma induced between the first and second electrodes within thisspace.

Preferably, the magnetic field generating means comprises first magneticfield generating means which comprises a plurality of magnet elementsdisposed so as to form a ring along half the circumference of which thedirection of magnetization of the magnet elements makes a completerotation as a whole, second and third magnetic field generating meanshaving a structure similar to that of the first magnetic fieldgenerating means disposed so as hold the first magnetic field generatingmeans between the second and third magnetic generating means such thatthe first, second and third magnetic generating means have the samecentral axis to thereby confine the plasma induced between the first andsecond electrodes to within this space.

Preferably, the magnet elements which compose the magnetic fieldgenerating means have different shapes and are arranged so as to form aring. The magnet elements which compose first magnetic field generatingmeans are arranged so as to form a ring along half the circumference ofthe which the direction of magnetization of the magnet elements makes acomplete rotation as a whole. Those magnet elements have differentshapes to confine a plasma induced between the first and secondelectrodes to within this space.

The first magnetic field generating means which comprises a plurality ofdifferent magnet elements arranged so as to form a ring along thecircumference of which the direction of magnetization of the magnetelements makes a complete rotation as a whole generates auni-directional magnetic field along and parallel to the secondelectrode to thereby induce a plasma within the vacuum container. Asecond magnet is disposed within the first magnetic field generated bythe magnetic field generating means to thereby increase the density ofthe plasma on the substrate by the second magnetic field generated bythe second magnet to process the substrate.

In the tenth aspect of the present invention, there is provided asurface processing device comprising a vacuum container provided with afirst electrode and a second electrode disposed opposite to the firstelectrode, the second electrode supporting thereon a substrate to beprocessed; gas feeding means for feeding a predetermined gas into thevacuum container; evacuating means for maintaining the inside of thecontainer at a reduced pressure; electric field generating means forgenerating an electric field in a region between the first and secondelectrodes; and magnetic field generating means for generating amagnetic field in the vacuum container, the magnetic field generatingmeans comprising a plurality of magnets arranged so as to form a ring insuch a manner that directions of magnetization thereof differ fromadjacent magnetic element by a predetermined phase making a 360 degreerotation along half the circumference of the ring, the magnetic fieldhaving a gradient of strength in an east-west direction of the ring.

Preferably, at least one second magnet is disposed within the magneticfield generated by the first magnet ring of magnet elements disposed soas to form a ring along half the circumference of which the direction ofmagnetization of the magnet elements makes a complete rotation as awhole such that the magnetic field has such a gradient that its strengthdecreases from the east of the ring toward its west.

Preferably, the magnetic field generating means comprises a plurality ofmagnet elements disposed so as to form a ring along half thecircumference of which the direction of magnetization of the magnetelements makes a complete rotation as a whole, the magnet elementsgenerating magnetic fields different in strength, the synthetic magneticfield having such a gradient that its strength decreases from the eastof the ring toward its west.

Preferably, the magnetic field generating means comprises a plurality ofmagnet elements disposed so as to form a ring along half thecircumference of which the direction of magnetization of the magnetelements makes a complete rotation as a whole, the magnet elementsmagnetic fields different in strength, the synthetic magnetic fieldhaving such a gradient that its strength decreases from the east of thering toward its west.

According to the tenth aspect of the present invention, the magnetelements composing the first magnetic field generating means or thesecond magnetic field generating means generate magnetic fieldsdifferent in strength so as to decrease the density gradient ofelectrons present in the plasma in the magnetic field space to therebyrender the plasma more uniform.

Damage due to electric charges borne on the substrate surface isreduced, While in the conventional device a completely uniform magneticfield cannot be obtained even by rotation of the magnetic field becausethe magnetic field is curved, the inventive arrangements are capable ofproviding a magnetic field completely parallel to and on the substrateto be processed, so that a complete uniform processing is established byrotation of the magnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 shows an etching device of a first embodiment of the presentinvention;

FIG. 2 shows an arrangement of a dipole ring used in the device of thefirst embodiment;

FIGS. 3(a) and 3(b) show the distribution of a magnetic field in theetching device;

FIGS. 4(a) and 4(b) show the steps carried out in the etching process bythe etching device;

FIGS. 5(a) and 5(b) show modifications of the arrangement of the dipolering;

FIG. 6 shows an etching device of the second embodiment of the presentinvention;

FIG. 7 shows the relationship between the phase difference between upperand lower dipole rings of the etching device of the second embodimentand the synthetic magnetic field generated by the upper and lower dipolerings;

FIG. 8 shows the relationship between the phase difference between theupper and lower dipole rings of the second embodiment and the syntheticmagnetic field generated by the upper and lower dipole rings;

FIGS. 9(a) and 9(b) show a rotation drive device for the upper and lowerdipole rings:

FIG. 10 shows an etching device of the third embodiment of the presentinvention;

FIGS. 11(a) and 11(b) show a rotation drive device for magnetic elementsof an etching device in the fourth embodiment of the present invention;

FIGS. 12(a) through 12(e) show the rotation and magnetic field directionof magnet elements in the fourth embodiment;

FIG. 13 shows a sputtering device according to the fifth embodiment ofthe present invention;

FIGS. 14(a) through 14(c) show the sputtering steps carried out in thefifth embodiment of the present invention;

FIG. 15 shows a CVD device according to the sixth embodiment of thepresent invention;

FIG. 16 shows a CVD device according to the seventh embodiment of thepresent invention;

FIGS. 17 shows to FIGS. 17(a) through 17(c) show the steps of making aMOSFET according to the eighth embodiment of the present invention;

FIG. 18 shows an etching device according to the ninth embodiment of thepresent invention;

FIG. 19 is an illustrative view of the essential portion of a dipolering of the etching device of the ninth embodiment;

FIG. 20 shows a dipole ring of the etching device according to the ninthembodiment;

FIGS. 21(a) and 21(b) show a distribution of magnetic field obtainedwhen the radius of the dipole ring is changed in the etching device ofthe ninth embodiment shown in FIG. 19;

FIG. 22 shows the relationship between the distance from the center of awafer and the magnetic field;

FIGS. 23(a) and 23(b) show the etching steps carried out by the etchingdevice of the ninth embodiment;

FIG. 24 shows the relationship between the distance between theelectrodes and the etching rate;

FIG. 25(a) and 25(b) show the etching steps carried out when theinventive device is used for etch-back purposes;

FIG. 26(a) through 26(d) show break down frequency and gate break downon a wafer for the inventive and conventional devices;

FIG. 27 shows a relationship between magnetic field, self bias voltage(Vdc) and etching rate;

FIG. 28 shows a relationship between magnetic field, etching rate andetch selectivity;

FIGS. 29(a) and 29(b) show the etching steps carried out in the ninthembodiment of the present invention;

FIG. 30 illustrates the essential portion of a dipole ring according tothe ninth embodiment of the present invention;

FIGS. 31(a) and 31(b) show the positions of parallel magnetic fields ofthe etching device for FIGS. 29(a) and 29(b) and the conventionaletching device;

FIG. 32 shows the relationship between the distance from the center of awafer and the etching rate when etching is performed using the dipolering of the ninth embodiment;

FIG. 33 shows an etching device according to the eleventh embodiment ofthe present invention;

FIGS. 34(a) through 34(c) show a dipole ring of the device of FIG. 33;

FIGS. 35(a) and 35(b) show a distribution of magnetic field of theetching device of the eleventh embodiment;

FIGS. 36(a) and 36(b) show an etching method using the etching device ofthe eleventh embodiment;

FIGS. 37(a) through 37(c) show a modification of the dipole ring;

FIGS. 38(a) through 38(c) show another modification of the dipole ring;

FIGS. 39(a) and 39(b) show still another modification of the dipolering;

FIGS. 40(a) and 40(b) show a modification of the dipole ring;

FIGS. 41(a) and 41(b) show a modification of the dipole ring;

FIG. 42 shows a modification of the dipole ring;

FIGS. 43(a) and 43(b) show a dipole ring according to the twelfthembodiment;

FIG. 44 shows the relationship between the distance from the center of awafer in and the etching rate of an etching device according to theeleventh embodiment of the present invention;

FIG. 45 shows the relationship between the distance from the center of awafer in and the etching rate according to the conventional etchingdevice:

FIG. 46 shows the relationship between the distance from the center of awafer and the etching rate when etching is performed using a dipole ringaccording to the twelfth embodiment of the present invention;

FIG. 47 shows the relationship between the difference in phase betweenthe upper and lower dipole rings and a magnetic field synthesized fromthe magnetic fields of the upper and lower dipole rings;

FIG. 48 shows the relationship between the difference in phase betweenthe upper and lower dipole rings and the magnetic field strength;

FIGS. 49(a) and 49(b) show a modification of the dipole ring;

FIGS. 50(a) and 50(b) show another modification of the dipole rings;

FIG. 51 shows an etching device according to the thirteenth embodimentof the present invention;

FIG. 52 shows a substrate to which etching is performed by the etchingdevice of the thirteenth embodiment;

FIGS. 53(a) and 53(b) show the distribution of the etching speed in thesurface of a wafer using the etching device of the thirteenthembodiment;

FIGS. 54(a) and 54(b) show the distribution of the etching speed in thesurface of a wafer using the etching device of the thirteenthembodiment;

FIG. 55 shows an etching device according to the thirteenth embodimentof the present invention;

FIGS. 56(a) through 56(c) show the distribution of the etching speed inthe surface of a wafer using the etching device of the fourteenthembodiment in comparison with the distribution using the conventionaldevice;

FIG. 57 shows a conventional magnetron etching device;

FIG. 58 shows the configuration of a wafer etched by the conventionalmagnetron etching device;

FIG. 59 shows a distribution of magnetic field in the conventionaldevice;

FIG. 60 shows the relationship between the distance from the center of awafer in and the etching rate of an etching device using a magnet of theconventional device; and

FIG. 61 shows the relationship between the distance from the center of awafer in and the etching rate of an etching device using a dipole ring.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described in detailhereinafter with respect to the accompanying drawings.

FIG. 1 shows an etching device of an embodiment of the presentinvention. The etching device comprises a first electrode 7 on the upperwall of a vacuum container 1, a second electrode 2 disposed opposite tothe first electrode 7 for acting also as a substrate support, a highfrequency power source 5 for applying electric power across the firstand second electrodes 7 and 2 through a matching circuit 14 to generatean electric field therebetween, and a dipole ring 13 disposed outsidethe vacuum container 1 for generating a magnetic field perpendicular tothe electric field and parallel to a surface of a wafer 3. A reactivegas is supplied through a gas inlet 4 into a region in which theelectric field and the magnetic field perpendicular to the electricfield exist so that plasma is generated by electric discharge. Aself-bias electric field (self bias voltage Vdc) is induced on the wafersurface which accelerates ions in the plasma to impinge on the wafer soas to advance the etching process.

FIG. 2 is a schematic plan view of the etching device of FIG. 1 in whichthe dipole ring 13 comprises magnet elements 30 disposed toconcentrically surround the outer cylindrical periphery of the vacuumcontainer 1. A magnet element 29 disposed at an angle of θ with respectto a magnet element 30₀ magnetized in the direction of magnetic field 35is magnetized in a direction which is rotated by 2θ from the directionof the magnetic field 35. The magnet element disposed at 180 degreeswith respect to the magnet element 30₀ is arranged such that thedirection of magnetization orients in the direction of magnetic field35. In order for the magnet elements to withstand twisting forces actingon them, they are fixed to a rigid non-magnetic yoke (not shown). Inorder to reduce a leakage magnetic flux, a yoke may be made of amagnetic material.

FIGS. 3(a) and (b) illustrates a magnetic field generated by the dipolering. As shown in FIGS. 3(a) and (b), the difference in the strength ofthe magnetic field between the central and peripheral portions of thewafer is within 20% and the tilt of the magnetic field with respect toan XY plane (the surface of the wafer) is less than ±5 degrees. In theheight direction, the difference in the strength of the magnetic fieldis within ±5% in 1/3 region of the central portion of the height of thedipole magnet elements and the tilt of the magnetic field is within 6degrees. By forming the cross section of the magnet elements circular orby increasing the number of magnet elements, further uniformity of themagnetic field can be achieved. In contrast, In the conventional deviceof FIG. 59, a ratio of the magnetic field strength of the central toperipheral portions of the magnet elements is two. Similarly, in aregion above the wafer, that is, in a region where a plasma is formed,the vertical magnetic field strength is larger in the peripheralportions so that the distribution of the plasma is distorted. The dipolering has been developed originally for use in a polarizer of SOR(Synchrotron Beam Orbital Radiation Facilities) or an medical devicesuch as MRI (Magnetic Resonance Imaging) device (K.Miyata et al: TheInternational Journal for Computation and Mathematics in Electrical andElectronic Engineering, Vol. 9(1990), Supplement A, 115-118, H.Zijlistra: Phillips J. Res. 40, 259-288, 1985). The inventors of thisapplication found that it is very effective to employ the dipole ring ina magnetized plasma producing device as in the present invention.

By perpendicular intersection between the electric field E and themagnetic field B, electrons in the plasma are drifted by the Lorentzforce in the direction of E×B so that the electrons run over a longerdistance. Thus, the frequency of the electrons to collide with neutralmolecules and atoms is increased and hence to the plasma density isincreased. Further, by only applying the magnetic field B to theelectrons, the electrons are confined within the plasma and the lifetimeof the electrons (the time period until the electrons collide with thesidewall of the chamber, the electrode or the wafer) is prolonged. As aresult, the plasma density is increased. This serves to not onlyincrease the etching rate but also improve the directivity of thoseions. Further, the ion energy which would amplify damage and reduce theetch selectivity can be suppressed at a sufficiently low level even ifthe gas pressure is reduced to suppress the reaction of neutral speciesand an etched film (isotropic reaction). In the second electrode 2 whichalso serves as the support of the substrate, a cooling fluid is suppliedthrough a pipe 17 so as to control the temperature of the substrate. Themagnetron plasma produced in the device of the present invention hashigh density and a quantity of heat given from the plasma to thesubstrate is larger than that in the conventional device.

The vacuum container 1 is constructed such that the first electrode 7 iselectrically isolated from the underlying wall of the container by aninsulator 11 disposed between the first electrode 7 and the underlyingwall of the container 1. However, the insulator 11 is not necessary whenthe first electrode 7 is grounded since the electric potential of thefirst electrode is equal to that of the container. Reference numeral 6denotes a reaction gas evacuating pipe and reference numeral 20 denotesan insulator which insulates the second electrode 2. A protective ring16 is disposed on the second electrode 2 so as protect the periphery ofa wafer on the second electrode 2 from being exposed to the plasma. Thematerial of the protective ring 16 is selected from the group ofceramics consisting of SiC, alumina, AIN and BN; carbons having variousstructures; Si; organic compounds; metals; and alloys, depending on afilm to be etched and a gas to be used.

Although a neodymium iron alloy (Nd--Fe) magnet is used in thisembodiment, permanent magnet materials such as Sm--Co material, ferriteor alnico may be used depending on a required magnetic field andrequired durability and weight of the magnet.

instead of providing the magnet above the vacuum container as in theconventional device of FIG. 57, the dipole ring 13 is provided aroundthe outer periphery of the sidewall of the container in the presentinvention. Thus, the back surface of the first electrode can be used fora monitor. A monitor 52 is provided above the vacuum container 1 formonitoring the state of a wafer surface such as etching depth through aquartz window 50 by using a laser detector 51.

The dipole ring 13 is movable in the vertical direction. A wafer isentered into or taken out from the vacuum container through a gate valve12 by a load lock mechanism (not shown) and a carrying mechanism (notshown) after the dipole ring 13 is lifted to a position shown in thebroken lines.

Alternatively, a mechanism for moving the second electrode 2 verticallymay be provided and a gate valve 12 is disposed at a heightcorresponding to a position where the second electrode 2 is lowered sothat a wafer is transferred into/out of the container by lowering theelectrode to the position below the dipole ring. Conversely, a mechanismmay be provided by which a wafer is transferred into/out of thecontainer at a position where the electrode is lifted relative to thedipole ring.

In this embodiment, by the arrangement of the dipole ring magnets, amagnetic field having a remarkable uniform strength can be generatedacross the opposite electrodes which produce a plasma. The magneticfield thus generated has a very strong flux of, for example, up toseveral kilogausses. Thus, the plasma density is increased and henceprocessing rate and performance are improved. The uniform processing onthe surface of a wafer is improved especially when the wafer has a largediameter. In addition, static break down of the MOS structure due tounevenness of the plasma is avoided. Since the magnet elements arearranged around the outer cylindrical periphery of the reactivecontainer, the upper portion of the container (on the anode side) can beopened for maintenance. This is also effective for monitoring theprocess or applying radio frequency Dower to the anode. Even when it isconstructed that the magnets and the wafer are rotatable relative toeach other to provide further uniformity, it is not necessary to movethe magnets in the event of maintenance as in the conventional device inwhich the magnets are disposed on the anode side. Further, the magnetscan be fixedly provided, for example, by means of a rail provided on theside of the reactive container. Thus, the handling of the device iseasy.

A method of etching a polycrystalline silicon film formed on a thinoxide film will be described by using the device of this embodiment.

Referring to FIG. 4(a), a wafer is constructed by forming a 10-nm thicksilicon oxide film and a polycrystalline silicon film 301 on a siliconsubstrate 300 and then forming a resist pattern 302 on the silicon film301. The wafer is carried onto the second electrode 2 within the vacuumcontainer 1 by a load lock mechanism and a carrying mechanism (both, notshown) after lifting the dipole ring 13. The wafer is then locked by astatic chuck (not shown) and the temperature is controlled to be at -30°C.

The dipole ring 13 is returned to its original position and the vacuumcontainer 1 is evacuated to about 10⁻⁶ Torr through the evacuatingsystem 6. A chlorine gas is then introduced at a rate of 100 cc/min.from the feed system 4 into the container 1. A high frequency (rf) powerof 250 W at 13.56 MHz is applied across the first and second electrodes7 and 2. The power density per a unit area of the cathode is 0.6 W/cm².The dipole ring 13 is then rotated at 200 rpm. The magnetic fieldstrength at this time within the dipole ring 13 is 200 G. The gas isthen evacuated by a vacuum pump (not shown) through a baffle (not shown)whose opening is covered with a metal mesh to prevent a wraparound ofthe plasma, discharge system 6 and a conductance valve whose exhaustingrate is adjustable with a variable opening percentage. The innerpressure of the chamber was set at 25 mTorr by adjustment of theconductance valve.

In the monitoring of the etching process, light emitted from the plasmais checked through the quartz window 50, a change in the density of thechlorine atoms which is the etching species is monitored to detect theend of a heavily phosphorus-doped polycrystalline silicon later. Afterpredetermined over-etching which includes prolongation of 20-100% of thenormal etching time to prevent the presence of unetched residues even ifthe etched film has a varying thickness, supply of the high frequencypower and the etching gas is stopped, the gas remaining in the chamberis evacuated, and the wafer is then taken out of the chamber by the loadlock mechanism.

The etching rate at this time is 345 nm/min. The etch selectivity to theunderlying silicon oxide film is 52, the etch selectivity to thephotoresist is 7, and uniformity is 3%. An etched configuration of thewafer having vertical cross section with high dimensional accuracy, asshown in FIG. 4(b) is obtained.

The etching process is performed without any dimensional conversionerror. Since the plasma density is maintained very high, the ion energyis suppressed low, a high etch selectivity is obtained, and damage isreduced.

In this embodiment, the dipole ring is rotated. However, the sameeffects can be achieved by rotating the second electrode and the wafer.

While in the embodiment the dipole ring 13 consists of 16 magnetelements, it may consist of 12 or 8 magnet elements, as shown in FIGS.5(a) and (b), respectively.

For the etching of a silicon oxide film, a gas including, for example,fluorocarbon (CF) may be used. For directivity processing of a resist, agas including oxygen as a main element may be used. For the etching ofaluminum used for interconnection, a gas including chlorine as a mainelement may be used. For the etching of other materials, a gas includingat least a reactive gas such as a halogen element or oxygen, hydrogen,nitrogen may be used.

The magnetic field strength is not limited to 200 gauss, but is selecteddepending on a material to be etched and a gas to be used. For example,when the magnetic field strength of 1,600 gauss is used for the etchingof phosphorus-doped polycrystalline silicon, the etch selectivity to theunderlying oxide film increases up to 74 while the etching rate is standunchanged. Under such strong magnetic field, a pressure range in whichthe magnetron discharge acts effectively is extended to 5×10⁻⁴ Torrthrough several hundreds of mTorr while in the conventional device thepressure range is about 8×10⁻³ Torr through 100 mTorr.

In the conventional device it is recognized that as a soap between theelectrodes is reduced to about 20 mm, the discharge efficiency isreduced. According to the present invention, under the magnetic fieldstrength of 1,600 gauss, the gap between the electrodes can be reducedup to 8 mm so as to increase the flexibility of design for the etchingdevice structure which is usually restricted by the requirements of theflow of a gas, etc. In addition, the frequency of the electric powerapplied across the electrodes is not limited to 13.56 MHz, but arelatively low frequency, for example, of about 100 kHz to 1 MHz iseffectively applicable for the etching of an oxide film which requires arelatively high ion energy depending on materials to be etched. For amaterial which requires to have a satisfactory etch selectivity to themask or the underlying material, such as the phosphorus-enrichedpolycrystalline silicon or an aluminum alloy, it is effective to use ahigh frequency of about 20-100 MHz and reduce the ion energy. In anycase, in a combination of the magnetic field strength, the ion energy,plasma density and other plasma parameters can be controlled.

As described above, the present invention is not limited to the aboveembodiment and is applicable to various devices.

A second embodiment of the present invention with a pair of upper andlower dipole rings will be described next.

Referring to FIG. 6, the dipole ring comprises an upper dipole ring 44and a lower dipole ring 45. A load lock chamber 42 communicates with acontainer 1 through a wafer carrying path 43 between the upper and lowerdipole rings 44 and 45 and through a gate valve 12 which isopened/closed by a gate valve opening/closing mechanism 41. The wafer ismoved into/out of the chamber through the load lock chamber 42, thewafer carrying path 43 and the gate valve 12. Reference numerals 46 and47 denote a gate valve drive shaft and a vacuum seal, respectively.

The remaining elements of the device are the same as the correspondingone of the first embodiment and the same reference numerals are used todenote the same elements in the first and second embodiments.

A method of etching to form a trench in a silicon substrate will bedescribed using the device of the second embodiment.

A Si substrate with the mask 302 of FIGS. 4(a) and (b) formed directlyon the Si substrate is placed in the load lock chamber 42, which is thenevacuated to about 10⁻⁶ Torr. The gate valve drive shaft 46 is loweredby the gate valve opening/closing mechanism 41 to open the gate valve12. The substrate is then carried through the wafer path 43 onto thesecond electrode 2, and fixed thereon by an electrostatic chuck (notshown), and the temperature is controlled to be 20° C. The gate valvedrive shaft 46 is then lifted by the gate valve opening/closingmechanism 41 to close the gate valve 12 and the container 1 is evacuatedto 10⁻⁶ Torr through the evacuating system 6. HBr gas is fed through thefeed system 4 at the speed of 200 cc/min with the pressure being kept at5×10⁻³ Torr. A high frequency Dower of 800 W is then applied across thefirst and second electrodes 7 and 2. The dipole rings 44 and 45 arerotated synchronously at the speed of 120 rpm. At this time, themagnetic field strength within the dipole rings 44 and 45 is 1,600 G.With the etching rate of 850 nm/min, a trench having vertical side wallsis formed in the Si substrate with high accuracy.

In the above-described manner, processing is performed with nodimensional conversion error. Since the plasma density is maintained atvery high level, the ion energy and hence damage are suppressed to below. It was found that the spacing between the upper and lower dipolerings contributes not only to the easiness for moving the wafer into thechamber but also to the uniformity of the magnetic field strength.

in the second embodiment, the upper and lower dipole rings which aremagnetized in equal direction are rotated synchronously. However, aphase difference may be provided between the upper and lower dipolerings such that the synthesis of the upper and lower magnetic fieldsresults in a given direction of magnetic field, as shown in FIG. 7.

FIG. 8 shows the relationship between the magnetic field strength andthe phase difference between the magnetized directions of the upper andlower dipole rings. By providing an appropriate phase difference betweenthe upper and lower dipole rings, the magnetic field strength can beadjusted to a desired value. A required magnetic field strength variesdepending on a process to be performed. By controlling the phasedifference by a pair of magnets, any required magnetic field can begenerated.

FIGS. 9(a) and (b) show a ring rotating mechanism provided between theupper and lower dipole rings 44 and 45 for controlling the rotation ofthese rings. Each of the rings 44 and 45 is provided with gears 74spaced along the outer periphery of a yoke 72 for fixing the magnets 71.The upper and lower dipole rings 44 and 45 (FIG. 6) are rotated with agear 74 which is engaged with both the gears 73 of the upper and lowerdipole rings. Each magnet takes the form of a square pillar. The gears73 are provided at several positions along the periphery of the yokedepending on the size and weight of the magnets. FIG. 9(b) shows across-sectional view of the device. The gear 73 is rotated with a shaft75 by a drive mechanism (not shown) and the torque is transmitted to thedipole rings via the gear 73. The dipole rings are rotated along a rail77 with a reduced friction by means of wheels 76 attached to a bearing79. The rail 77 is provided in the form of a ring below the dipole ringsand connected to the vacuum container 1 through an upper/lower drivemechanism 96 (FIG. 10). With this arrangement, high speed rotation ofthe dipole rings is possible. It is to be noted that small parts such asbearings are omitted in the drawings of this embodiment. The upperdipole ring 44 may be suspended from above instead of being supported bythe rail from below. Since the upper and lower dipole rings 44 and 45exert a complicated force on each other, the gears which drive the upperand lower rings may be fixed to a single shaft 75 to achieve completesynchronous rotation.

By changing the engaging position of the gears or by providing removablecoaxial gears, the rotational speed or relative phase of the upper andlower rings can be changed. By adjusting the relative phases of magnetsof the upper and lower rings, the magnetic field strength can easily beadjusted without replacement of the magnets with different magnets.Further, by rotating the upper and lower dipole rings in oppositedirections with the same rotational axis, an alternate magnetic fieldcan be generated without replacing the magnets.

Alternatively, it may be designed such that each magnet element has itsown motor, and under electric control, each magnet element may besynchronously rotated with each other or asynchronously rotated witheach other so that not only the magnetic field is rotated but also analternate magnetic field is generated. Further, the alternate magneticfield can be rotated and the strength and distribution of the magneticfield can be changed.

When the magnetic field is rotated at a high speed, the strength of themagnetic field may be reduced by eddy currents generated by traversingthe magnetic field through a conductor. Therefore, A device in which astrong magnetic field is rotated at a high speed, a vacuum containershould be made of a high resistance material or an insulating material.In addition, by making a part or all of the first or second electrodeusing a paramagnetic material, the magnetic flux becomes easy to passtherethrough. As a result, the magnetic field can be corrected at aplace such as the periphery of the electrodes where the magnetic fieldis likely to be distorted.

A third embodiment of the present invention will now be described inwhich a device has a magnet assembly containing a built-in high speedrotational mechanism and an upper/lower mechanism for the magnetassembly.

Referring to FIG. 10, lower and upper dipole ring assemblies 91 and 92rotatable at a high speed are provided along the outer peripheralsurface of a vacuum container 1 through a vertical position and spacingadjusting mechanism 96. The dipole ring assemblies 91 and 92 arerespectively accommodated in housings 98 provided with a duct hose 97 toprevent dust or particles from being discharged the outside of theassemblies during the rotation. Provided in the upper portion of thevacuum container 1 are gas emission nozzles 93 and gas discharge holes94. The gas discharge through the gas discharge nozzles 94 is evacuatedupward through an evacuating system 6. The remaining structure issimilar to the corresponding one of the second embodiment.

In a fourth embodiment of the present invention, magnet elements whichconstitute the magnetic field generating means are disposed such thatthe magnetized direction of each magnetic element deviates from eachother by a predetermined phase. Each magnet element is independentlyrotated to thereby form a magnetic field equivalent to that which wouldbe generated by the rotation of the overall magnet assembly.

Referring to FIG. 11, a ring 103 has teeth on the inner and outerperipheral surfaces thereof. Sixteen small gears 102 are provided suchas to engage with the inner surface teeth of the ring 103. Cylindricalmagnet elements 101 are attached to respective lower faces of the gears102. A gear 105 engaged with the teeth of the outer peripheral surfaceof the ring 103 is connected to a rotation drive mechanism 104.Reference numerals 106 and 107 denote a pedestal and a bearing,respectively.

In this embodiment, the rotation drive mechanism 104 rotates the ring103 around a center B. As a result, the individual magnet elements 101and hence the resulting synthetic magnetic field rotate. By clockwiserotation of a drive motor (not shown) in the rotation drive mechanism104, the ring 103 and the magnet elements 101 rotate counterclockwise.As a result, the synthetic magnetic field 108 rotates clockwise.

With the rotation drive mechanism 104, it is possible to rotate thesynthetic magnetic field by individually rotating each of the magnetelements on its own axis without changing the respective positions ofthe magnet elements.

FIG. 12(a) illustrates an arrangement of the magnetic elements in whichthe magnetized directions of the magnet elements are the same in thoseof FIG. 2 although the shape of the magnet elements is different. Itwill be seen from FIGS. 12(b) through 12(e) that as the individualmagnet elements are rotated clockwise at the same speed, the syntheticmagnetic field rotates counterclockwise, and that the rotational angleof the magnet elements and that of the synthetic magnetic field coincidewith each other. With this arrangement, the same effect is obtained asthat which would be obtained by the rotation of large dipole ring,without actually rotating the large dipole ring.

A sputtering device as a fifth embodiment of the present invention willbe described next.

Referring to FIG. 13, the sputtering device comprises a target plate 61attached to a first electrode 7 which is, in turn, attached to an upperwall of a container 1 and a second electrode 2 disposed opposite to thetarget 61. The second electrode 2 also serves as a support of asubstrate. A direct current power source 64 applies a DC voltage to thetarget plate 61 while a high frequency source 5 supplies a highfrequency electric power to the second electrode 2 via a matchingcircuit 14 to generate an electric field in a region therebetween. Inthis region, a magnetic field is generated perpendicular to the electricfield by upper and lower dipole rings 44 and 45 disposed outside thevacuum container 1. Gas is supplied into that region from a gas feedsystem 4, and a plasma is generated by electric discharge. Ions in theplasma impinge on the target plate 61 and sputtering particles from thetarget plate 61 are guided to a wafer 3 on the second electrode 2 insuch a manner that the particles moves vertically to the wafer 3. Thedistance between the target plate 61 and the second electrode 2 isselected to be 3 cm.

The dipole rings 44 and 45 are similar in structure to those of thesecond embodiment of FIG. 6. The magnetic field generated by the dipolerings 44 and 45 is parallel to the surface of the target 61. Theinteraction E×B of the magnetic field and the electric field formed onthe surface of the target plate serves to maintain the magnetrondischarge. The electrons in the plasma produced by the magnetrondischarge are drifted to improve the ionizing efficiency to therebygenerate a high density plasma even under a relatively low pressure.

A temperature adjusting mechanism 62 for controlling the temperature ofthe substrate may comprises a heater embedded in the second electrode 2.

The upper vacuum container wall is insulated from the lower portion ofthe container wall by an insulator 65 disposed between the upper andlower portion of the container wall in the vicinity of the firstelectrode 7. Reference numerals 6 and 63 denote an evacuating system anda temperature adjusting mechanism for cooling the target plate 61,respectively.

The transfer of a wafer into/out of the vacuum container 1 is made by aload lock mechanisms (not shown) and a carrying mechanism (not shown).

A method of forming a film using this device will be described below.

Referring to FIG. 14(a), a wafer comprises a silicon substrate 68 with apattern 67 being formed on the surface thereof. The wafer is carriedonto the second electrode 2 within the vacuum container 1 by the loadlock mechanism and conveyance mechanism (both not shown), fixed by aelectrostatic chuck (not shown), and controlled so as to be at a desiredtemperature of 250° C.

The container 1 is then evacuated by the evacuating system 6. Argon gasis then fed at a flow rate of 100 cc/m into the container 1 through thefeed system 4 until the pressure in the container 1 becomes 10⁻³ Torr.In order to eliminate pollutant such as an oxide film and a hydrocarbonon electrodes of the wafer surface, a high frequency power is applied tothe second electrode 2 to generate a plasma and to clean the wafersurface before the sputtering process. A large Dower is then applied tothe target to sputter an aluminum alloy. That is, a direct current power(400 V, 3.5 A) is applied to the target plate 61 (first electrode 7) anda high frequency power is applied to the second electrode 2 to therebydischarge the argon gas to form a plasma. Electrons are confined by themagnetic field a region between the electrodes. As a result, thelifetime of electrons and the travel distance of the electrons areincreased. Thus, the frequency of the electron collision with moleculesand atoms increase and hence the ionizing efficiency increase to therebyform a plasma of high density even under a low gas pressure. Therotational speed of the magnetic field is 200 rpm in the presentembodiment for the same reason as in the embodiment directed to theetching process.

Drop in the cathode voltage (Vdc) occurs on the surface of the targetplate 61, which is irradiated with argon ions in the plasma, so thatparticle of the target plate 61 material or deposited material, forexample aluminum, are discharged into the plasma to be sputtered againstthe wafer. Incidentally, since the cathode voltage (Vdc) has a negativevalue, when the drop in the cathode voltage occurs, the absolute valueof the cathode voltage increases.

Since the high frequency power applied to the second electrode 2generates a biasing voltage to the substrate and deposition andsputtering of the aluminum occur simultaneously on the surface of thesubstrate, the aluminum particles are guided efficiently into the bottomof grooves as shown in FIG. 14(b). In the device of this embodiment, astrong magnetic field completely parallel to the substrate surface isgenerated and the target is decreased uniformly. Thus, a good uniformfilm is formed over the overall wafer surface without producing "voids"within the film. Depositing rate is 1.7 μm/min. and a film uniformity of±3% is achieved.

In the conventional device, when there is a local high density plasmaregion, a part of the target plate is subjected to high speedsputtering. Therefore, lifetime of the target plate is shortened, andthe resulting film is not uniform and the shape of the film varies fromposition to position in the wafer. In contrast, according to thisembodiment, the region where a high density plasma is formed covers theoverall target plate. Since the target can be uniformly sputtered, theperformance is improved and damage is reduced.

By performing etch-back as shown in FIG. 14(c), embedded layers 69 witha good film quality are formed even in fine grooves.

As described above, a high density plasma is generated even under arelatively low pressure of about 10⁻³ Torr so that contamination intothe film is greatly reduced to thereby improve the film quality. Inaddition, the depositing rate is increased. Under a low pressure, themean free path of the particles increases, which improves thedirectivity of moving deposited chemical species.

In addition of the formation and etching of a thin aluminum film, thisdevice is applicable to the formation and etching of various thin filmssuch as a high melting point thin film, for example, of tungsten ormolybdenum, and an insulating film, for example, of aluminum oxide,tantalum pentoxide, aluminum nitride, silicon oxide or silicon nitride.

The structure and materials of the device are not limited to those ofthis embodiment and are modifiable when required without departing fromthe spirit and scope of the present invention.

A cold-wall type plasma CVD device as a sixth embodiment of the presentinvention will next be described.

Referring to FIG. 15, the CVD device is characterized by amultiple-dipole ring assembly 51 consisting of first through fourthdipole rings disposed around the outer periphery of the container 1.

The device comprises a first electrode 7 disposed upper portion of thecontainer 1 and a second electrode 2 disposed opposite to the firstelectrode 7. The second electrode 2 also serves as a support of asubstrate. Gas is fed toward a wafer 3 on the second electrode 2 througha gas inlet 4 provided in the vicinity of the first electrode 7. A highfrequency electric power produced by a high frequency source 5 isapplied across the first and second electrodes 7 and 2 through amatching circuit 14 to produce a self-biasing electric field in a regionbetween the first and second electrodes 7 and 2. In this region, amagnetic field is generated by the multi-dipole ring assembly 51disposed around the vacuum container 1. the magnetic field isperpendicular to the electric field and parallel to the surface of thewafer 3. A high density plasma is formed in that region. Ions in theplasma is accelerated by the self-biasing electric field induced on thewafer surface and impinge on the wafer to proceed the formation of athin film.

Disposed above the container 1 are a temperature adjusting mechanism 53which adjusts the temperature of the first electrode 7, and a powersource 59 connected through a matching circuit 58 to the first electrode7. Reference numerals 54, 55, 56 and 57 denote a quartz window, opticaldetector, optical fibre, and a spectrometer which disperses light from aplasma and examines the gaseous phase.

The formation of a thin film using this device will be described next.

Depositing gas of SiH (200 cc/min.) and O₂ (200 cc/min.) are fed intothe container 1, and electric discharge is conducted under a pressure of8×10⁻⁴ Torr to form a thin SiO₂ film. The wafer is carried in the samemanner as in the above embodiments. The load lock mechanism is notshown. The first electrode is provided separately from the container 1and connected to the separate power source 59. The gas is fed uniformlyagainst a wafer from gas introducing nozzles 52 through the inside ofthe first electrode. The basic sequence of operations is similar to thatin the above devices.

The process is characterized as follows. Depositing seeds formed in theplasma are deposited like snow piles and absorbed on a surface of thewafer. Reaction is advanced by the impact of ions which are acceleratedby the, biasing voltage induced by a high frequency power from the powersource 5. With the process, a film with reduced impurities and a smallrefractive index and close to a thermal oxide film is finally formed. Inthis embodiment, a very high magnetic field of 2000 gauss is applied.The high frequency power is 1.2 kW and the depositing rate is 0.3μm/min.

When the value of the magnetic field strength is very high as in thisembodiment, the difference between the high and lower magnetic fieldstrengths becomes large even if highly uniform magnets are used. Inorder to code with such situation, a 4-divided type dipole ring assemblyis used in the present embodiment. This magnet assembly can finelyadjust the magnetic field strength and distribution by adjusting theposition of the uppermost or lowermost magnet. When the device becomeslarge as the wafer has a large diameter, the distance between thecentral portion of the electrode and the container wall differs greatlyfrom the distance between the peripheral portion of the electrode andthe container wall, so that the plasma characteristics differ. Theuniformity of the plasma can be improved by intentional disturbance ofthe magnetic field in the peripheral portions of the first and secondelectrodes while the magnetic field strength in the vicinity of thewafer is maintained. The multi-magnet arrangement of this embodiment hassuch applications.

As described above, by carrying the present invention in the CVD device,improvement to the film forming rate and magnetic strength uniformity,and reduction in damage are achieved to form a high density plasma.Since decomposition and reaction of the gas advances in the gas phase,improvement in the quality of the film such as reduction in the mixedimpurities and improvement in the density was recognized.

As a seventh embodiment of the present invention, a hot wall type plasmaCVD device will be described next.

Referring to FIG. 16, the CVD device is characterized by a cylindricalheater 78, a cooling cylinder 75 and a cooling pipe 79 provided on theouter periphery of a vacuum container 71 made of a quartz pipe, and adipole ring 80 provided around the outer periphery of the cooling pipe79. Generally, the magnetic materials have a Curie point of severalhundreds of ° C. The coercive force of many of these magnetic materialstend to decrease from about 100° C. and a rise in temperature wouldcause a deterioration in the characteristic. To avoid such situation,cooling means is provided in devices where heat is generated, forexample, in a CVD device or an etching device where the chamber isheated.

The gas inlet and outlet 74 and 76 are provided at opposite ends of thevacuum container such that wafers 73 are disposed perpendicular to theflow of the gas through the inlet and outlet. Reference numeral 72denotes first electrodes supported by an electrode support 82. Referencenumeral 77 denotes second electrodes supported by an electrode support82 opposite to the first electrodes. Reference numeral 5 denotes a powersource.

A process for making a MOSFET using the FIG. 1 etching device as aneighth embodiment of the present invention will be described next.

As shown in FIG. 17(a), element isolating areas 122 and then a gateisolating film 123 were formed on a surface of a silicon substrate 121.An n⁺ polycrystalline silicon film 124 was then formed by CVD. A resistpattern 125 was then formed on the film 124.

Thereafter, this silicon substrate was set in the etching device ofFIG. 1. As shown in FIG. 17(b), the n⁺ polycrystalline silicon film 124was subjected to anisotropic etching with the resist pattern 125 as amask. The etching gas used was a mixed gas of Cl₂ +H₂ ; the pressure was30 mTorr; and the applied power was 200 W. By the use of this device,the wafer surface was exposed to plasma, so that it bore electriccharges. If the voltage (electric charges) due to the electric chargesis uniform through the wafer surface, no high voltage is applied acrossthe thickness of the gate oxide film. Thus, gate break down wasprevented. Thus, sufficient etch selectivity was obtained to therebyform a pattern of high dimensional accuracy.

Thereafter, ion implantation was effected with the gate electrode as amask to form a source-drain area 126; and the resist pattern was removedto form a MOSFET.

As described above, according to the present invention, finehighly-reliable MOSFETs are obtained without break down of the gateelectrodes.

A ninth embodiment of the present invention will be described next.

FIGS. 18 and 19 show an etching device according to the presentinvention in which the same elements as in FIG. 1 is given the samereference numerals and detailed description for these elements areomitted. The device is characterized in that the diameter of a dipolering 13 is changeable and the lower electrode 2 is movable up and downusing an electrode level setting means 30. That is, arrangement is suchthat a substrate to be processed is fed by its vertical movement into amagnetic field generated by the dipole ring 13 composed of a pluralityof different magnets which are arranged in the form of a ring along halfthe circumference of which the direction of magnetization of the magnetsmakes a complete rotation.

The etching device, the whole of which is shown diagrammatically in FIG.18, is provided with a first electrode 7 which includes the upper wallof the vacuum container 1 and a second electrode 2 which is disposedopposite to the first electrode 2 so as to be movable up and down andalso functions as a substrate support. An electric power generated bythe high frequency source 5 is applied across the first and secondelectrodes 7 and 2 through a matching circuit 14 to produce an electricfield. A reactive gas is fed through a gas inlet 4 into a space wherethe electric field is perpendicular to a magnetic field parallel to asurface of a wafer 3 and formed by a dipole ring 13 disposed outside thevacuum container 1 and the resulting plasma is confined by electriccharging; ions accelerated out of the plasma by a self-biasing electricfield induced on the wafer surface impinge on the wafer to advance theetching reaction.

FIGS. 19 and 20 show an enlarged illustrative view of an essentialportion of the dipole ring 13 viewed from above and an overallillustrative view, respectively. The dipole ring 13 is provided withmagnets 30 concentrically surrounding the outer periphery of thecontainer 1 and supported such that the diameter of the ring 13 isvariable. A magnet M₁₆, disposed at an angle of θ to a magnet 30₀magnetized in the direction of magnetization 35 is magnetized in adirection which is rotated by 2 relative to the direction ofmagnetization 35. A magnet disposed at an angle of 180 degrees to themagnet 30₀ is disposed along the circle so as to have the direction ofmagnetization 35 again. Since forces act on the individual magnets whichare components of the ring to twist them, they are fixed to a stubbornnon-magnetic yoke (not shown), which may instead be a magnetic yoke toreduce a leakage magnetic field furthermore.

According to this structure, since the second electrode is movable upand down, the substrate to be processed is easily lowered and conveyedwhen required. Therefore, it is unnecessary to provide separate magneticgenerating means. Thus, a reduction in the magnetic field which wouldotherwise occur is prevented and no auxiliary magnetic field applied toprevent such reduction is required. Thus, the device may have a simplestructure to form a uniform high density magnetic field. The plasmapotential and self-bias are equalized and highly anisotropic uniformsurface processing can be performed on the surface of the substrate tobe processed.

The height of the cathode electrode which is the second electrode onwhich the substrate 3 is placed may be set to any position; theinter-electrode spacing is changeable to an optimal one during plasmaprocessing depending on the material of the wafer, the gas and thepressure to thereby change the processing characteristic.

By changing the diameter of the ring along which the magnets arearranged, the magnetic field strength produced within the ring can bechanged as desired; and control of the ion energy can cause a change inthe processing characteristic.

FIGS. 21(a) and (b) show the distribution of magnetic field generated bythe dipole ring when the diameter of the ring is changed by 60 mm. Asshown in these Figures, by moving the magnets in the radial direction ofthe dipole ring, the magnetic field strength is easily changed.

In order to describe the operation of the device according to thepresent invention, FIG. 22 shows a distribution of magnetic fieldproduced by the dipole ring magnets. In this case, it is assumed thatthe substrate to be processed is conveyed with the ring having a slit athalf the height of the ring to move the wafer into/out of the container.As will be obvious from FIG. 22, uniform is achieved such that thedifference between the magnetic field strengths produced by the dipolemagnet in the central and peripheral portions of the wafer is less than20%; and that the tilt of the magnetic field in a XY plane is less than5 degrees. In the axial direction of the dipole ring, the magnetic fieldwas suppressed to within ±5% in the central ring portion of the dipolemagnet which is 1/3-2/3 of the overall height of the magnet and the hiltof the magnetic field was suppressed to within ±6 degrees. Furthermore,uniformity of this magnetic field is further improved by using magnetshaving a circular cross section and increasing the number of suchmagnets. However, the magnetic field strength is lowered by providingthe slit in the peripheral portion of the chamber wall. In order toprevent such situation, an auxiliary magnet would be additionallyprovided for correcting purposes, so that the device structure wouldbecome very complicated. However, as in the above embodiment structures,provision of the second electrode movable up and down greatly simplifiesthe device structure to eliminate correction by additional provision ofthe auxiliary magnet.

By perpendicular intersection between the electric field E and themagnetic field B, as just described above, Lorentz force driftselectrons in the plasma, generated by the magnetron discharge, in thedirection of E×B over a long distance to thereby increase the frequencyof the electrons to collide with neutral molecules and atoms and henceincrease the plasma density. Further, by only applying the magneticfield B to those electrons, these electrons are confined within theplasma to prolong their lifetime (the time taken for the electrons tocollide with the sidewall of the chamber, electrode and wafer).Furthermore, the plasma magnetic field strength is increased at the Nand S poles to confine the plasma. As a result, the plasma density isfurther increased. This serves to not only increase the etching rate butalso improve the directivity of those ions. Furthermore, the ion energywhich would otherwise amplify damage and reduce the etch selectivity aremaintained sufficiently low even if the gas pressure is reduced suppressthe reaction of neutral seeds and an etched film (isotropic reaction).

Furthermore, a fluid is fed through a cooling pipe 17 in the secondelectrode 2 as the substrate support to thereby control the temperatureof the substrate efficiently. This is because the magnetron plasmaproduced by the present invention has high density and a quantity ofheat emitted from the plasma to the substrate is large compared to theconventional device.

The vacuum container is constructed such that the first electrode 7 iselectrically isolated from the lower portion of the container by aninsulator 11 disposed in the vicinity of the first electrode 7.Reference numerals 4 and 6 denote a reaction gas feeding system and anevacuating system, respectively. Reference numeral 20 denotes aninsulator which insulates the second electrode. A protective ring 16 isdisposed on the second electrode so as protect the periphery of a waferon the second electrode 2 from direct exposure to the plasma. Thematerial of the protective ring 16 is selected from the group ofceramics consisting of SiC, alumina, AIN and BN; carbons having variousstructures; Si; organic compounds; metals; and alloys, depending on theetched film and gas used.

While in the embodiment neodymium (Nd--Fe) magnets are used, a permanentmagnet material such as a Sm--Co material, ferrite or alnico may beselected and used in consideration of required magnetic field,durability and weight.

As just described above, the arrangement of the dipole ring magnetsresults in a markedly uniform magnetic field between the oppositeelectrodes which produce a plasma and also provides a high magneticfield strength, for example, of up to several kilogausses, compared tothe conventional device. Thus, the plasma density is improved and henceprocessing rate and characteristic are improved. The uniformity of asurface of wafer is further improved especially when the wafer has alarge diameter. In addition, static break down of the MOS structure of awafer which would otherwise be caused due to unevenness of the plasma isavoided, advantageously. Since the magnets are arranged around the outerperiphery of the cylindrical side of the reactive container, the upperportion of the container (on the anode side) which is required to beopened in maintenance can be opened. This is also effective formonitoring the process or applying radio frequency power to the anode.Even when the magnets and a wafer are rotatable relative to each otherto provide further uniformity, no movement of the magnets is required inmaintenance as is in the conventional device with the magnet disposed onthe anode side. Thus, the magnets are fixedly attached, for example, bya rail provided on the side of the reactive container and the device iseasy to handle.

A method of etching actually a silicon oxide film formed on a siliconsubstrate using the present device will be now described.

First, as shown in FIG. 23(a), a 1000-nm thick silicon oxide film 301 isformed on the silicon substrate 300. Further, a resist pattern 302 isthen formed on the silicon film 301. This half-finished product ishandled as a wafer, which is carried onto the second electrode 2 withinthe vacuum container 1 by a load lock mechanism and a carrying mechanism(both, not shown); it is then locked by a static chuck (not shown); andthe wafer and the second electrode are then lifted together to aposition 27 mm from the first electrode.

The vacuum container 1 is evacuated to about 10⁻⁶ Torr by the evacuatingsystem 6. A CF₄ gas is then introduced at a rate of 50 cc/min. from thefeed pipe 4 into the container 1. A high frequency (rf) power of 200 Wat 13.56 Mhz is applied across the first and second electrodes 7 and 2.The power density a unit area of the susceptor at this time is 0.6W/cm². In this case, the dipole ring 13 is not rotated, but may berotated. The magnetic field strength at this time within the dipole ring13 is 200 G.

When the etching is completed, supply of the high frequency power andthe etching gas are stopped, the gas remaining in the chamber isevacuated, the second electrode is lowered to its original position, andthe wafer is then taken out of the chamber by the load lock mechanism toprovide an etched appearance of the wafer having a vertical crosssection with high dimensional accuracy, as shown in FIG. 24(b).

In this way, processing is achieved without any dimensional conversionerror. In addition, since the plasma density is maintained very high,the ion energy is suppressed low, high etch selectivity is obtained, anddamage is reduced.

While in the embodiment the dipole ring is composed of 16 magnets, itmay be composed of 12 or 8 magnets, as shown in FIG. 5.

While a gas including fluorocarbon (CF) was used to etch the siliconoxide film, a gas including mainly oxygen may be used to process thedirectivity of the resist. A gas mainly including chlorine may be usedto process with high performance aluminum used for wiring purposes. Inthese cases, the effects produced by the present invention wereascertained. Other materials may be etched with a gas including at leasta reactive gas such as a halogen element or oxygen, hydrogen, nitrogen.

The magnetic field strength is not limited to 200 gauss, and is selectedsuitably depending on a material to be etched, and a gas to be used.

Furthermore, it was conventionally recognized that a reduction in theinter-electrode spacing to about 20 mm resulted in a reduction in thedischarge efficiency while a reduction in the inter-electrode spacing to8 mm was achieved under 1,600 gauss, so that an acceptable limit of thedevice structure required for the flow of the gas is increased. Inaddition, the high frequency is not limited to 13.56 MHz, but arelatively low frequency of about 100 KHz to 1 MHz is effective foretching an oxide film which requires a relatively high ion energyalthough it depends on the etched material. In order to reduce the ionenergy, the use of a high frequency of about 20-100 MHz is effective fora material, which is required to have a satisfactory etch selectivity tothe mask or the underlying material, such as the phosphorus-enrichedpolycrystalline silicon or an aluminum alloy. In either case, in acombination of the magnetic field strength, the ion energy, plasmadensity and other plasma parameters can be controlled.

By changing the vertical movement distance of the second electrode 2using this device, the electrode distance is changed to 27, 40 and 55 mmsequentially, and the silicon oxide film formed on the silicon substratewas actually etched, the result of which is shown in FIG. 24. As will beobvious from FIG. 24, a change in the inter-electrode distance changesthe etching rate and the uniformity of the magnetic field. As justdescribed above, by changing the inter-electrode distance, depending onthe material to be etched, less-damage etching or higher speed etchingis selected.

The inter-electrode may be changed during this etching and sequentialetching may be performed.

As just described above, the present invention is not limited to theabove embodiments, and is applicable to various devices.

For example, when an insulating film is formed on an electrode of a MOSdevice and etch-back is performed for flattening purposes by an etchingdevice which uses a conventional magnet, uneven electric charging can beperformed on the wafer surface due to uneven magnetic field generated bythe conventional magnet. As a result, insulation brakeage occurs in theperiphery of the wafer. In contrast, with the inventive device, electriccharges is uniform on the wafer surface to thereby prevent theoccurrence of insulation break down.

As the evaluation of damages, FIG. 25 show a result of the process whichincludes the step of forming an insulating film 304 (thin oxide film of100 angstrom) on a silicon substrate 303, depositing a CVD oxide film306 on a gate electrode of a MOS structure on which a polycrystallinesilicon film 305 is deposited, and flattening the resulting surface ofthe MOS structure by etching-back.

A substrate is conveyed onto the second electrode 2 within the vacuumcontainer 1 by the load lock mechanism and conveyance mechanism; fixedby the static chuck (not shown); and then lifted to a position 27 mmfrom the first electrode 7 which is the center of the dipole ring.

The vacuum container 1 is then evacuated by the evacuating system 6 toabout 10⁻⁶ Torr; a CF₄ gas is fed at a rate of 50 cc/min. from the feedsystem 4 into the container; 1,027 W (2.7 W/cm²) of a high frequencypower at 13.56 MHz is applied across the first and second electrodes 7and 2; the CVD oxide film is etched; the high frequency power is thenturned off; the feed of the etching gas is stopped; the gas remainingwithin the chamber is evacuated; the second electrode is lowered to itsoriginal position; the load lock mechanism is again used to take thesubstrate out of the chamber to thereby provide an etched substrate asshown in FIG. 25(b).

FIGS. 26(a) and (b) respectively show break down frequency and gatebreak down on the wafer surface in this device occurring when anelectric field of a 8 MV/cm is applied across the wafer. These Figuresexhibited that there occurred no gate break down until the applied fieldarrived at 15 MV/cm and hence there occurred no gate break down untilthe applied field arrived at 8 MV/cc. FIGS. 26(c) and (d) show breakdown frequency and gate break down on a wafer surface in theconventional device which occurred when an electric field of 8 MV/cm wasapplied across the wafer, respectively. FIGS. 26(c) and (d) show thatgate break down occurred when the applied field was 5 MV/cm or less, andgate break down occurred at 10 places out of 82 places in the peripheralportion of the wafer by the time when the applied field arrived at 8MV/cm.

FIG. 27 shows graphs indicative of the relationship of magnetic field,oxide film etching rate, and self bias voltage measured when etching wasperformed under the same conditions. It will be known from this resultthat as the magnetic field strength increases, the etching rateincreases, and the self bias voltage decreases.

A further embodiment will be described below in which the diameter ofthe dipole magnet ring and the magnetic field strength are changed. FIG.28 shows a polysilicon etching rate obtained when the diameter of thering, and hence the magnetic field strength were changed under theconditions similar to those in the eight embodiment, and etching wasperformed. The etching gas used was Cl₂, 150 W (0.5 W/cm ²) of highfrequency power at 13.56 MHz was applied to the wafer; and the pressurewas maintained at 50 mTorr. As the magnetic field increases, the etchingrate does not increase monotonously and is maximum at a magnetic fieldstrength of about 400 G. It was found that when the etching rate of asimilar oxide film was measured to try to obtain the etch selectivity, asatisfactory etch selectivity was obtained at a magnetic field strengthof 500 G.

Etching was sequentially performed using these magnetic field strengths.A silicon oxide film 308 was deposited on a silicon substrate 307, apoly-silicon film 309 was deposited by 400 nm by CVD, and a photoresist310 was patterned to provide a wafer (FIG. 29(a)).

This wafer is carried onto the second electrode 2 within the vacuumcontainer 1 by the load lock mechanism and the carrying mechanism; it isthen locked by the static chuck (not shown); and the wafer and thesecond electrode are then lifted together to a position 27 mm from thefirst electrode.

The vacuum container 1 is evacuated to about 10⁻⁶ Torr through theevacuating system 6. A Cl₂ gas is then introduced at a rate of 50cc/min. from the feed system 4 into the container 1. A high frequency(rf) power of 150 W (0.5 W/cm²) at 13.56 Mhz is applied across the firstand second electrodes 7 and 2 so that the magnetic field strength is 400G to adjust the diameter of the dipole ring to etch the poly-siliconfilm.

Immediately before the underlying silicon oxide film 308 is exposed, thediameter of the dipole ring is reduced such that the magnetic field is500 G to thereby perform over-etching.

When the etching is completed, supply of the high frequency power andthe etching gas are stopped, the gas remaining in the chamber isevacuated, the second electrode is lowered to its original position, andthe wafer is then taken out of the chamber by the load lock mechanism toprovide a satisfactory etched appearance of the wafer, as shown in FIG.29(b).

As described above, the etching rate is initially set at a high value,the magnetic field strength is halfway increased and etching isperformed with high etch selectivity, so that high rate etching isperformed with a high etch selectivity maintained.

A tenth embodiment of the present invention will next be described inwhich the height of a space for a parallel magnetic field is changed. Inthis embodiment, the dipole ring 13 of FIGS. 18 and 20 is provided witha plurality of magnets M1-M16 arranged so as form a ring in which thedirection of magnetization of the magnets makes a complete rotationalong half the circumference in a plane perpendicular to the axis of thering. Three sets of the magnets, M16, M1, M2 and M8, M9, M10, have thedirection of magnetization toward the central axis of the ring and thestrengths of the magnets are substantially the same but the directionsare opposite. As shown in FIG. 31(a), with this arrangement, theparallel magnetic field generated by the dipole ring 13 can bepositioned deviated from the center of the dipole ring 13. For comparingpurposes, FIG. 31(b) shows the position of the parallel magnetic fieldgenerated by the arrangement of FIG. 18 which contains no directionalcomponents perpendicular to the ring.

For example, a parallel-magnetic field can be generated at a positionwhich is 5 cm lower than the midpoint height of the dipole ring 13. Evenat that position, uniformity is obtained which corresponds to thedistribution of the magnetic field at the midpoint of the conventionaldipole ring, that is, the distribution of the magnetic field in the XYspace is less than 15%, and the distribution of the vertical componentsis less than 4%.

As shown in FIG. 32, this device also provides uniformity similar tothat obtained by the use of the conventional dipole ring. Generation ofa parallel-magnetic field space in any position within the ring providesthe characteristic which the conventional dipole ring has and greatlyreduces the vertical distance through which the wafer is driven, and thewafer conveyance mechanism is greatly simplified compared to theconventional device.

The vertical components may greatly be changed during etching.

While in the above embodiments magnetic generating means such as thedipole rings was provided outside the vacuum container, they may beprovided inside.

The present invention is effective not only for processing electricalparts directly, but also similarly for film formation or surfaceprocessing on an already formed electric part or for film formation andsurface processing of lead electrodes connected to the underlyingelectric parts. The electric parts are not limited to MOS structures.They include all electric parts which have electrical functions and aredeteriorated by voltages and currents applied thereacross and flowingtherethrough, respectively; that is, pn junctions, transistors andcapacitors having various structures.

Another application is implantation of impurities into the substrate. Aparallel-flat plate type plasma device is used. A gas which containsboron, for example, a BF₃ gas, is fed into the plasma device and aplasma is generated. A gas in the plasma is dissociated in the plasmaand the B atoms are implanted into the substrate. At this time, sincethere are many F atoms, the gas pressure is reduced to 10⁻⁵ Tort toprevent etching by the F atoms. By applying the magnetic field as in thepresent invention, a plasma is generated even at such a low gas pressureand the ion energy is suppressed to about scores of several eV to 300 eVto thereby form a very shallow impurity layer. Also in the presentinvention, effects such as uniformity or a reduction in damage aresimilarly realized.

FIGS. 33 and 34 show an etching device of an eleventh embodiment of thepresent invention.

The etching device is characterized in that two pairs of upper and lowerauxiliary magnets 23a and 23b are disposed in the direction of N-S linesof magnetic force within a pair of upper and lower dipole rings 13a and13b so as to provide an increased magnetic field at the peripheralportion of the container to confine a plasma satisfactorily within themagnetic field. FIG. 33 shows a diagrammatic overall structure of thedevice; FIGS. 34(a) and (b) are respectively a horizontalcross-sectional view and a vertical side cross-sectional view of theessential portion of the device of FIG. 33; and FIG. 34(c) shows asynthetic magnetic field formed by the pair of dipole rings and the twopairs of auxiliary magnets.

The etching device is provided with a first electrode 7 which includesthe upper wall of the vacuum container 1 and a second electrode 2 whichis disposed opposite to the first electrode 2 and also functions as asubstrate support. An electric power generated by the high frequencysource 5 is applied across the first and second electrodes 7 and 2through a matching circuit 14 to produce an electric field. A reactiveGas is fed through a gas inlet 4 into a space where the electric fieldis perpendicular to a magnetic field parallel to a surface of a wafer 3and formed by dipole rings 13a, 13b and auxiliary magnets 23a, 23bdisposed outside the vacuum container 1 and the resulting plasma isconfined by electric charging; ions accelerated out of the plasma by aself-biasing electric field induced on the wafer surface impinge on thewafer to promote the etching reaction.

FIG. 34(a) shows an illustrative view of the essential portions of thedipole rings 13a, 13b of FIG. 33 viewed from above. The dipole rings13a, 13b each is provided with magnets 30 concentrically surrounding theouter periphery of the cylindrical container 1. A magnet disposed at anangle of θ to a magnet 30₀ magnetized in the direction of magnetization35 is magnetized in a direction which is rotated by 2 θ relative to thedirection of magnetization 35. A magnet disposed at an angle of 180degrees to the magnet 30₀ is disposed along the ring so as to have thedirection of magnetization 35 again. Since forces act on the individualmagnets which are components of the ring to twist them, they are fixedto a stubborn nonmagnetic yoke (not shown), which may instead be amagnetic yoke to reduce a leakage magnetic field.

FIGS. 35(a) and (b) illustrates a distribution of magnetic fieldproduced by this dipole ring. As will be obvious from FIGS. 35(a) and(b), the difference in the strengths of the magnetic fields produced bythe dipole magnets between the central and peripheral portions of thewafer can be suppressed to within 20%. Uniformity is such that the tiltof the magnetic field in an XY plane can be suppressed so as to be lessthan ±5 degrees. In the axial direction of the container, the differencein magnetic field can be suppressed to within ±5% in the centralportions of the dipole magnets which involve 1/3-2/3 of their overallheight and the tilt of the magnetic field is suppressed to within ±6degrees. The use of magnets having a circular cross section or anincreased number of magnets will contribute to the formation of afurther uniform magnetic field. In contrast, the conventional device ofFIG. 57 has a ratio of more than 2 in magnetic field strength of theperipheral to central portions of the wafer. Similarly, in theconventional device, even above the wafer or even in a region where aplasma is formed, the vertical magnetic field strength is largerespecially in the peripheral portion of the wafer than in its centralportion to thereby disturb the distribution of the plasma.

Furthermore, a fluid is fed through a cooling pipe 17 in the secondelectrode 2 as the substrate support to thereby control the temperatureof the substrate efficiently. This is because the magnetron plasmaproduced by the present invention has high density and a quantity ofheat emitted from the plasma to the substrate is large compared to theconventional device.

The vacuum container is constructed such that the first electrode 7 iselectrically isolated from the lower portion of the container by aninsulator 11 disposed in the vicinity of the first electrode 7.Reference numerals 4 and 6 denote a reaction gas feeding system and anevacuating system, respectively. Reference numeral 20 denotes aninsulator which insulates the second electrode. A protective ring 16 isdisposed on the second electrode so as protect the periphery of a waferon the second electrode 2 from direct exposure to the plasma. Thematerial of the protective ring 16 is selected from the group ofceramics consisting of SiC, alumina, AIN and BN; carbons having variousstructures; Si; organic compounds; metals; and alloys, depending on theetched film and gas used.

While the magnet is provided above the vacuum container in theconventional device, the dipole rings 13a, 13b are provided around theouter periphery of the sidewall of the container in the presentinvention. Thus, the back of the first electrode can be used for amonitor or the like. Therefore, the monitor 52 which monitors the stateof a wafer surface and more particularly the etching depth through aquartz window 50 by means of a laser detector 51 is provided above thevacuum container 1.

The dipole rings 13a, 13b have therebetween a slit through whichmovement of a wafer into/out of the vacuum container is performedthrough a gate valve 12 by a load lock mechanism and a carryingmechanism after the auxiliary magnets 23a, 23b are lifted to a position(shown in the dotted line).

Alternately, a mechanism which moves the second electrode vertically maybe provided and a gate valve may be provided at a position where thegate valve is lowered to move a wafer into/out of the container, suchthat the electrode is lowered and the wafer is processed. Conversely, amechanism may be provided which moves a wafer into/out of the containerat a position where the electrode is lifted relative to the dipolerings.

As just described above, the arrangement of the dipole ring magnetsresults in a markedly uniform magnetic field between the oppositeelectrodes which produce a plasma and also provides a high magneticfield strength, for example, of up to several kilogausses, compared tothe conventional device. Thus, the plasma density and hence processingrate and characteristic are improved. The uniformity of a surface ofwafer is further improved especially when the wafer has a largediameter. In addition, static break down of the MOS structure of a waferwhich would otherwise be caused due to unevenness of the plasma isavoided, advantageously. Since the magnets are arranged around the outerperiphery of the cylindrical side of the reactive container, the upperportion of the container (on the anode side) which is required to beopened in maintenance can be opened. This is also effective formonitoring the process or applying radio frequency power to the anode.Even when the magnets and a wafer are rotatable relative to each otherto provide further uniformity, the movement of the magnets is notrequired in maintenance as is in the conventional device with the magnetdisposed on the anode side. Thus, the magnets are fixedly attached, forexample, by a rail provided on the side of the reactive container andthe device is easy to handle.

A method of etching actually a silicon oxide film formed on a siliconsubstrate using the present device will be now described.

First, as shown in FIG. 36(a), a 1000-nm thick silicon oxide film 301 isformed on a silicon substrate 300. Further, a resist pattern 302 is thenformed on the silicon film 301. This half-finished product is handled asa wafer, which is carried through between the dipole rings 13a, 13b ontothe second electrode 2 within the vacuum container 1 by a load lockmechanism (both, not shown) and a carrying mechanism and it is thenlocked by a static chuck (not shown).

The vacuum container 1 is evacuated to about 10⁻⁶ Torr through theevacuating system 6. A CF₄ gas is then introduced at a rate of 50cc/min. from the feed system 4 into the container 1. A high frequency(rf) power of 200 W at 13.56 Mhz is applied across the first and secondelectrodes 7 and 2. The power density a unit area of the susceptor atthis time is 0.6 W/cm². In this embodiment, the dipole rings 13a, 13bare not rotated. However, they may be rotated. The magnetic fieldstrengths at this time within the dipole rings 13a, 13b are 200 G. Thegas is then evacuated by a vacuum pump (not shown) through a baffle (notshown) whose opening is covered with a metal mesh to prevent awraparound of the plasma into the opening, evacuating system 6 and aconductance valve whose discharge rate is adjustable with a variableopening percentage. The inner pressure of the chamber was set at 40mTorr by adjustment of the conductance value.

When etching is completed, supply of the high frequency power and theetching gas is stopped, the gas remaining in the chamber is evacuated,and the wafer is then taken out of the chamber by the load lockmechanism to thereby providing a satisfactory etched configuration ofthe wafer having a vertical cross section with high accuracy, as shownin FIG. 36(b).

In this way, processing is achieved without any dimensional conversionerror. In addition, since the plasma density is maintained very high,the ion energy is suppressed low; high etch selectivity is obtained; anddamage is reduced.

In order to etch the silicon oxide film, a gas including, for examplefluorocarbon (CF), was used. In order to process the directivity of aresist, a gas including mainly oxygen may be used. Aluminum used forwiring purposes may be processed with high performance with a gasincluding chlorine mainly. The effects produced by the present inventionwere ascertained even in those modifications. Alternatively, etching maybe achieved with a gas including at least a reactive gas such as ahalogen element, oxygen, hydrogen or nitrogen.

The magnetic field strength is not limited to 200 gauss, and is selectedsuitably depending on a material to be etched, and a gas to be used.

Furthermore, it was recognized that a reduction in the inter-electrodespacing to about 20 mm resulted in a reduction in the dischargeefficiency in the conventional device while a reduction in theinter-electrode spacing to 8 mm under 1,600 gauss was achieved, so thatan acceptable limit of the device structure required for the flow of agas was increased. In addition, the high frequency is not limited to13.56 MHz, but a relatively low frequency of about 100 kHz to 1 MHz iseffective for etching an oxide film which requires a relatively high ionenergy although it depends on the etched material. In order to reducethe ion energy, the use of a high frequency of about 20-100 MHz iseffective for a material, which is required to have a satisfactory etchselectivity to the mask or the underlying material, such asphosphorus-doped polycrystalline silicon or an aluminum alloy. In eithercase, in a combination of the magnetic field strength, the ion energy,plasma density and other plasma parameters can be controlled.

As described above, the present invention is not limited to theembodiment and is applicable to various devices.

A wafer was empirically etched in the eleventh embodiment and therelationship between the distance from the center of the wafer and theetching rate was measured. As a result, it was found that uniformity ofthe etching rate was greatly improved in the N-S direction, as shown inFIG. 44. FIG. 45 shows the result of a similar experiment using theconventional etching device with no magnetic field gradient forcomparing purposes,

While in the tenth embodiment, the two pairs of auxiliary magnets areprovided, a modification may be such that as shown in FIGS. 37(a)-(c) apair of auxiliary magnets 23 may be provided in the N-S direction in themagnetic field produced by the first magnetic generating means composedof dipole rings 13a, b. Also, in this case, a magnetic field is obtainedwhich is parallel to a surface of a wafer 3 placed in the magneticfield. As shown in FIG. 37(c), the peripheral magnetic field isincreased to thereby confine the plasma to within the magnetic field.

As shown in FIGS. 38(a)-(c), the magnets having the same direction ofmagnetization as the first magnetic field generation means are strongerin magnetic force than others. Thus, also in this case, a magnetic fieldparallel to the surface of the wafer 3 is obtained. The peripheralmagnetic fields at those magnets are higher than the other field tothereby confine the plasma satisfactorily to within the magnetic field.

FIG. 39 shows a change in the angle of the magnets in the N-S directionand having the same direction of magnetization as the dipole rings ofthe embodiments. In the conventional dipole rings, the magnet disposedat θ to the direction of magnetization 40 has the direction ofmagnetization rotated by 2 θ from the direction of magnetization 40.Magnetization in which the angle x<2 θ as shown in FIG. 39(a) increasesthe magnetic field in the direction of connection of the magnetic polesto thereby confine the plasma, as shown in FIG. 39(b).

FIGS. 40(a), (b) show the arrangement of three dipole rings 13p, 13q and13r having the same structure and same central axis with the upper andlower dipole rings 13p, 13r having the direction of magnetizationrotated 180 degrees from that of the intermediate ring 13q. A wafer 3 isplaced in the magnetic field produced by the intermediate ring 13q.According to this arrangement, the magnetic field from the intermediatering is canceled partly at the center of the wafer by the magneticfields generated by the upper and lower dipole rings 13p, 13r, so thatthe central magnetic field is weaker than the peripheral one to therebyconfine the plasma satisfactorily.

FIGS. 41(a), (b) show a modification where the shapes of magnetsconstituting a dipole ring are successively changed such that themagnets at N and S poles are longest. Thus, the magnetic field densitiesat the N and S poles are maximum to thereby confine the plasmasatisfactorily. Even if the length of the magnets at the N and S polesis minimum, confinement of the plasma on the wafer is achievedsatisfactorily. If a longer magnet is thinner, and a shorter magnet isthicker to make the respective strengths of the magnets equal, a leakagemagnetic field is reduced.

FIG. 42 shows a structure of two stacked dipole rings having a minimumdimension in the Z direction to thereby increase the peripheral magneticdensity. By all those structures, plasmas can be confined more or less.

A twelfth embodiment of the present invention will next be describedwhere the respective magnetic strengths of the magnets which constitutea dipole ring are changed with a gradient of magnetic field strength inthe E-W direction to thereby provide a gradient of the electron densitypositively.

In FIGS. 43(a), and (b), the magnetic field strengths of the magnets ofa dipole ring are larger in the vicinity of the E pole and smaller inthe vicinity of the W pole such that there is a gradient from the E tothe W to thereby prevent collection of electrons in the plasma near theW pole and hence an increase in the local reactivity.

The remaining structure is the same as the corresponding one of theprevious embodiments.

A wafer was etched by this device under the same conditions as in theeleventh embodiment and the relationship between the distance from thewafer center and the etching rate was measured. As a result, it will beunderstood that the etching rate is uniform in the W-E direction, asshown in FIG. 46. FIG. 45 shows the result of a similar experiment usinga conventional etching device with no gradient of magnetic fieldstrength for comparing purposes. Preferably, correction to both thelengths of the magnets and the gradient of the magnetic field strengthin the E-W direction improves both the uniformity of the etching ratesin the N-S and E-W directions.

According to this device, processing without dimension conversion errorsis achieved. In addition, since the plasma density is maintained veryhigh, the ion energy and hence damage are suppressed low.

While in the eleventh embodiment the upper and lower dipole rings havingthe same direction of magnetization are rotated synchronously, the upperand lower dipole rings may have a phase difference such that thesynthetic magnetic field has a given direction, as shown in FIG. 47.

FIG. 48 shows the result of measurement of the relationship between themagnetic field strength and the difference in magnetization directionbetween the upper and lower magnets. The provision of the upper andlower dipole rings having a different phase difference therebetweenserves to adjust the magnetic field strength. Although the requiredmagnetic field strength varies depending on a process to be performed,control of the phase difference by a set of magnets provides a requiredmagnetic field.

FIG. 49 shows a modification of the eleventh embodiment where two groupsof opposing auxiliary magnets 23 alternate in magnetization directionare arranged in the magnetic field of the magnets constituting a dipolering 13 to thereby increase the magnetic field strengths in theperipheral portions of a wafer to confine a plasma and hence compensatefor a possible decrease in the etching rate there. When in the presentarrangement the dipole ring is rotated relative to the substrate to beprocessed since the two groups of auxiliary magnets are provided in theN-S direction which is the magnetized direction of the dipole ring,either the auxiliary magnets may be rotated in phase with the dipolering or the auxiliary magnets may be rotated with only the dipole ringfixed.

Similar effects will be produced by a ring arrangement of a plurality ofauxiliary magnets 23 alternate in polarity within a dipole ring 13, asshown in FIG. 50. In this case, the plurality of auxiliary magnets 23 isnot required to be rotate, for example, may be fixed to either the inneror outer wall of the vacuum container even when the dipole ring 13 isrotated.

According to the present invention, improvements to the film formingspeed and uniformity of magnetic field strength, reduction in damages,and the formation of a high density plasma are achieved. Since thedecomposition and reaction of a gas in the gaseous phase advance, thequality of the formed film is improved.

The thirteenth embodiment of the present invention will be described inwhich a magnetron RIE layer provided with dipole ring magnets capable ofchanging a slit interval therebetween is used. Etching is performedwhile the slit interval is changed.

Referring to FIG. 51, dipole rings 401 and 402 are movable vertically toset the interval therebetween at a desired value. A test wafer comprisesa silicon substrate and a 1,100 nm thick oxide film formed thereon isfed onto a cathode electrode 2 in a etching chamber (vacuum container) 1by a load lock mechanism (not shown) and is fixed by a electrostaticchuck (not shown). After setting the slit interval between the dipolerings 401 and 402 at a desired value, CF₄ is fed into the chamber 1 at aflow rate of 100 SCCM and the internal pressure of the chamber 1 isadjusted to be 0.5 mTorr. A high frequency power of 13.56 MHz is appliedto the cathode electrode 2 with an electric power of 2.7 W/cm². Theetching is performed for 60 seconds. The etched wafer is then taken ofthe chamber 1 by the load lock mechanism and the distribution of theetching rates on the etched wafer surface are measured. FIGS. 53 and 54show distribution of etching rates in the wafer with respect to the slitinterval. FIG. 53(a) shows distribution of the etching rates for a zeroslit interval. Since the magnetic field in the chamber 1 becomes amirror magnetic field when the slit interval is zero, the etching rateat the center of the wafer is very high compared with the periphery ofthe wafer. FIG. 53(b) shows the distribution for 5-mm slit interval. Asthe small slit interval is provided, the mirror magnetic field weakensso that the concentration to the center of the wafer weakens. As aresult, uniformity of the distribution becomes improved compared withzero slit interval although the etching rate is still high at thecenter. FIG. 54(a) shows the distribution for 10-mm slit interval. Inthis case, the magnetic field strength in the chamber 1 is substantiallyuniform and the uniformity of the etching rate distribution is greatlyimproved. FIG. 54(b) shows the distribution for 30-mm etching interval.In this case, although the magnetic field strength is uniform in aregion directly above the wafer, it decreases in a region near the innerchamber wall. This causes the etching rate to be decreased in thevicinity of the wafer periphery. The optimum slit interval variesdepending on the factors such as the inner diameter of the chamber andthe dipole rings as well as the strength and shade of magnet elementsconstituting the dipole rings. Therefore, by selecting the slit intervalconsidering the above-mentioned, uniform etching can be performed.

A fourteenth embodiment of the present invention will be described inwhich a dividing member for dividing the space in the vacuum containeris provided around the outer periphery of a wafer to be processed.

Referring to FIG. 55, a dividing member 601 takes the form of a hollowcylinder and is provided such as to surround a cathode 3 on which thewafer is placed. The dividing member 601 divides the inner space of thecontainer Into a region 603a where the wafer 602 is placed and a region603b where no substrate to be processed is placed. The dividing member601 is made of a porous material with pores 601a having a diameter ofapproximately 5 mm through which gas is evacuated out of the region603a. The dividing member 601 may be made of a net with mesh ofapproximately 1 mm. The material of the dividing member 601 may beselected among metals such as aluminum whose surface is almetized andinsulating materials such as ceramics. When the dividing member 601 ismade of a metal, it may be grounded or kept at a predeterminedpotential.

Etching of the wafer 602 by using this device will be described next.The wafer 602 comprising a silicon substrate 501 and a 1100-nm thickoxide film 502 formed thereon as shown in FIG. 52 is conveyed from aload chamber (not shown) onto a cathode electrode 2 within the etchingchamber (vacuum container) 1 and fixed by a electrostatic chuck (notshown). After setting the slit interval between the dipole rings 401 and402 at a desired value, CF₄ is fed into the chamber 1 at a flow rate of100 SCCM and the internal pressure of the chamber 1 is adjusted to be0.5 mTorr. A high frequency power of 13.56 MHz is applied to the cathodeelectrode 2 with an electric power of 2.7 W/cm² . The etching isperformed for 60 seconds. The etched wafer is then taken of the chamber1 by the load lock mechanism and the distribution of the etching rateson the etched wafer surface are measured.

FIG. 56(a) shows the etching rate distribution for zero slit intervalbetween the dipole rings 604a and 604b in which the magnetic filed inthe chamber 1 in a mirror magnetic field so that the density of plasmaat the center of the wafer 602 is high and the etching rate at thecenter of the wafer 602 is very high compared to the periphery of thewafer 601. FIG. 56(b) shows the etching rate distribution in which aslit is provided between the dipole rings. In this case, no mirrormagnetic field is formed and the etching rate is uniformly distributedaround the center of the wafer. However, the magnetic field strength isgreatly reduced near the inner wall of the chamber due to the slit sothat the etching rate is reduced near the inner wall.

Then, the wafer 602 is etched by the magnetron RIE device having thedividing member 601 and a slit between the dipole rings 604a and 604b asshown in FIG. 55. The dividing member 601 is arranged such that electricdischarge takes place only in a limited region of directly above thewafer 602 and where the magnetic field strength formed by the dipolerings is uniform. FIG. 56(c) shows the distribution of etching rate inthe wafer surface in this etching process. In this case, etching isperformed only in the space where a uniform magnetic field is presenteven in the etching at a low pressure of approximately 0.5 m Torr and isnot influenced at all by the reduction in the magnetic field in thevicinity of the inner wall of the chamber.

In the above two embodiments, CF₄ is used as a reactive gas. However,CF₄ /H₂ may be used.

Although the dipole rings are provided outside the vacuum container inthe above embodiments, it may also be provided inside the container.

The present invention is applicable not only for processing electricparts directly, but also for film formation and surface processing onelectric parts formed on a substrate and for film formation and surfaceprocessing for lead electrodes to be connected to underlying eclecticparts on the substrate. The electric parts are not limited to MOSstructures, but include any electric parts such as pn junctionstructure, transistors and capacitors having various structures whichhave electrical functions and are likely to be damaged by voltage andelectric current applied thereacross and flowing therethrough.

Another application of the present invention includes the implantationof impurities into a substrate. A gas which contains boron such as BF₃gas is fed into a parallel-plate type plasma device for generatingplasma therein. The gas is dissociated in the plasma and B atoms areimplanted into the substrate. At this time, since a great number of Fatoms are present, the gas pressure is reduced to 10⁻⁵ Torr to preventthe etching. By applying the magnetic field as in the present invention,plasma is generated even at a low gas pressure and the energy of ions issuppressed to a level about several tens to 300 eV so that a veryshallow impurity layer can be formed. In this embodiment, uniformity ofthe magnetic filed and reduction of damage are also realized.

While the present invention was described with respect to the embodimentof the magnetron plasma processing device and method which mainlyhandles etching, CVD, film formation by sputtering, impurityimplantation, using a dipole ring, the present invention is not limitedto the embodiment, and is applicable to other processes and deviceswhich use other magnetizing plasmas. For example, the magnetic fieldstrength is selected in a range of scores--thousands of gauss, dependingon a process effected.

The present invention is usable in plasma CVD devices; sources of plasmaions for devices which improve wafer surfaces using a plasma, and forion implantation devices; devices which generate ECR or Whistler(Helicon) wave plasmas and use them as sources of plasma, electrons,ions or neutral active seeds.

In the arrangements, a high frequency or direct current power may beapplied to the individual first and second electrodes. While the highfrequency used was 13.56 MHz in many cases, such frequency may beselected in a range of a low frequency of about 100 kHz to a higherfrequency of several hundreds of MHz depending on application to therebyadjust the magnetic field strength and ion energy.

Concerning a pair of opposing two magnetic elements in the dipole ring,one of the opposing magnetic elements is not necessarily positioned atthe opposing position (180 degree rotating position) of the other one ofthe opposing magnetic elements as long as the direction of the magneticfield at the opposing position is equal to the magnetization directionof the other one of the magnetic elements. For example, it may be soarranged that the direction of the synthetic magnetic field generated bytwo magnetic elements adjacent to the opposing position is equal to themagnetization direction of the other one of the magnet elements.

What is claimed is:
 1. A plasma generating apparatus comprising:a vacuumcontainer provided with a first electrode and a second electrodedisposed opposite to said first electrode; gas feeding means for feedinga predetermined gas into said vacuum container; evacuating means formaintaining the inside of said container at a reduced pressure; electricfield generating means for supplying electric power between said firstand second electrodes to generate an electric field in a region betweensaid first and second electrodes; and magnetic field generating meansfor generating a magnetic field in said vacuum container, said magneticfield generating means comprising a plurality of magnetic elementsarranged in a circle around said container so as to form a ring, each ofsaid magnetic elements having an axis directed to a center of saidcircle and a magnetization direction, wherein one of said magneticelements is so disposed that the magnetization direction thereofcoincides with the axis thereof, and each of said magnetic elementsother than said one magnetic element is so disposed that an angle of themagnetization direction thereof relative to the magnetization directionof said one magnetic element is substantially twice an angle of the axisthereof relative to the axis of said one magnetic element.
 2. A surfaceprocessing apparatus comprising:a vacuum container provided with a firstelectrode and a second electrode disposed opposite to said firstelectrode for supporting thereon a substrate to be processed; gasfeeding means for feeding a predetermined gas into said vacuumcontainer; evacuating means for maintaining the inside of said containerat a reduced pressure; electric field generating means for supplyingelectric power between said first and second electrodes to generate anelectric field in a region between said first and second electrodes; andmagnetic field generating means for generating a magnetic field in saidvacuum container, said magnetic field generating means comprising aplurality of magnetic elements arranged in a circle around saidcontainer so as to form a ring, each of said magnetic elements having anaxis directed to a center of said circle and a magnetization direction,wherein one of said magnetic elements is so disposed that themagnetization direction thereof coincides with the axis thereof, andeach of said magnetic elements other than said one magnetic element isso disposed that an angle of the magnetization direction thereofrelative to the magnetization direction of said one magnetic element issubstantially twice an angle of the axis thereof relative to the axis ofsaid one magnetic element.
 3. A surface processing apparatus accordingto claim 2, further comprising rotating means for rotating said magneticfield generating means around a central axis thereof relative to saidsubstrate to be processed.
 4. A surface processing apparatus accordingto claim 2, wherein said magnetic field generating means comprises aplurality of magnetic elements arranged around the other periphery ofsaid container so as to form a ring in such a manner that directions ofmagnetization thereof differ from adjacent magnetic element by apredetermined phase making a 360 degree rotation along half thecircumference of said ring, whereby a plasma is generated.
 5. A surfaceprocessing apparatus according to claim 2, further comprising movingmeans for moving said magnetic field generating means along central axisthereof.
 6. A surface processing apparatus according to claim 2, whereinsaid magnetic field generating means comprises at least two separatemagnetic field generating sub-means disposed such as to have the samecentral axis, at least one of said magnetic field generating sub-meansbeing movable along said central axis.
 7. A surface processing apparatusaccording to claim 2, wherein said magnetic field generating meanscomprises at least two separate magnetic field generating sub-meansdisposed such that distance between said two magnetic field generatingsub-means is adjustable.
 8. A surface processing apparatus according toclaim 6 or 7, wherein said magnetic field generating means comprises atleast two separate magnetic field generating sub-means disposed suchthat the difference in phase between said two magnetic field generatingsub-means is adjustable.
 9. A surface processing apparatus according toclaim 2, further comprising rotating means for rotating each of saidplurality of magnetic elements.
 10. A surface processing apparatusaccording to claim 2, further comprising electrode position settingmeans for moving said second electrode to change the distance betweensaid first and second electrodes.
 11. A surface processing apparatusaccording to claim 2, further comprising diameter changing means forchanging the diameter of the ring formed by said plurality of magnetelements.
 12. A surface processing apparatus according to claim 2,wherein at least one pair of opposing magnet elements have directionelements along a central axis of said ring, magnetic strengths of saiddirection elements are equal to each other with direction thereofopposite to each other.
 13. A surface processing apparatus according toclaim 2, further comprising a fence member provided around periphery ofsaid substrate to be processed.
 14. A surface processing apparatusaccording to claim 2, wherein magnetization strengths of said magneticelements are adjusted in such a manner that the strength in anorth-south direction of the magnetic field in said vacuum containeraround the peripheral portions of said substrate is equal to or greaterthan that of the magnetic field at the center of said substrate.
 15. Asurface processing apparatus according to claim 2, further comprising aplurality of complementary magnets provided in the vicinity of said ringin such a manner that the strength in a north-south direction of themagnetic field in said vacuum container around the peripheral portionsof said substrate is equal to or greater than that of the magnetic fieldat the center of said substrate.
 16. A surface processing apparatusaccording to claim 2, wherein the magnetic field in said vacuumcontainer has a gradient of strength in an east-west direction of saidring.
 17. A surface processing apparatus according to claim 2, furthercomprising a plurality of complementary magnets provided in the vicinityof said ring in such a manner that the magnetic field in said vacuumcontainer has a gradient of strength in an east-west direction of saidring.
 18. A surface processing apparatus according to claim 2, whereinat least one of said magnetic elements is displaceable so as to be ableto adjust a strength of the magnetic field generated by the magneticfield generating means.
 19. A surface processing apparatus according toclaim 2, wherein at least one of said magnetic elements disposed in thevicinity of said one magnetic element and in the vicinity of a positionrotated by 180 degrees from said one magnetic element has amagnetization direction such that an angle between the magnetizationdirection thereof and the magnetization direction of said one magneticelement is smaller than twice an angle between an axis thereof and theaxis of said one magnetic element.
 20. A surface processing apparatusaccording to claim 2, wherein said magnetic field generating meanscomprises three rings having the same structure and disposed coaxiallyone over another, an intermediate one of said rings being disposed byrotating 180 degrees relative to upper and lower ones of said rings. 21.A surface processing apparatus according to claim 2, wherein saidplurality of magnetic elements include a second magnetic elementdisposed at a position 180 degrees from said one magnetic element, saidposition corresponding to an S pole of said magnetic field generatingmeans while a position at which said one magnetic element is locatedcorresponds to an N pole of said magnetic field generating means, themagnetic elements having lengths along a central axis of the magneticfield generating means which are successively decreased as the magneticelements are disposed farther apart from a closer one of said onemagnetic element and said second magnetic element, said one magneticelement and said second magnetic element having the same length, whichis greater than the lengths of the remaining magnetic elements.
 22. Asurface processing apparatus comprising:a vacuum container provided witha plurality of reactive chambers; a first electrode provided in at leastone of said reactive chambers; a second electrode provided opposite tosaid first electrode; gas feeding means for feeding a predetermined gasinto said at least one reactive chamber; evacuating means formaintaining the inside of said at least one reactive chamber at areduced pressure; electric field generating means for supplying electricpower between said first and second electrodes to generate an electricfield in a region between said first and second electrodes; and magneticfield generating means for generating a magnetic field in said at leastone reactive chamber, said magnetic field generating means comprising aplurality of magnetic elements arranged in a circle around said at leastone reactive chamber so as to form a ring, each of said magneticelements having an axis directed to a center of said circle and amagnetization direction, wherein one of said magnetic elements is sodisposed that the magnetization direction thereof coincides with theaxis thereof, and each of said magnetic elements other than said onemagnetic element is so disposed that an angle of the magnetizationdirection thereof relative to the magnetization direction of said onemagnetic element is substantially twice an angle of the axis thereofrelative to the axis of said one magnetic element.
 23. A surfaceprocessing method comprising the steps of:placing a substrate to beprocessed on a second electrode disposed opposite to a first electrodein a vacuum container; feeding a predetermined gas into said vacuumcontainer; generating an electric field in a region between said firstand second electrodes; and forming a uni-directional magnetic fieldsubstantially parallel to a surface of the substrate to be processed bymeans of a plurality of magnetic elements arranged in a circle aroundthe vacuum container so as to form a ring, each of said magneticelements having an axis directed to a center of said circle and amagnetization direction, wherein one of said magnetic elements is sodisposed that the magnetization direction thereof coincides with theaxis thereof, and each of said magnetic elements other than said onemagnetic element is so disposed that an angle of the magnetizationdirection thereof relative to magnetization direction of said onemagnetic element is substantially twice of an angle of the axis thereofrelative to the axis of said one magnetic element, thereby to induce aplasma within the vacuum container to process the surface of thesubstrate.
 24. A plasma generating apparatus comprising:a vacuumcontainer provided with a first electrode and a second electrodedisposed opposite to said first electrode, for carrying thereon asubstrate to be processed; gas feeding means for feeding a predeterminedgas into said vacuum container; evacuating means for maintaining theinside of said container at a reduced pressure; electric fieldgenerating means for supplying electric power between said first andsecond electrodes to generate an electric field in a region between saidfirst and second electrodes; magnetic field generating means forgenerating a magnetic field in said vacuum container, said magneticfield generating means comprising a plurality of magnetic elementsarranged in a circle around said container so as to form a ring, each ofsaid magnetic elements having an axis directed to a center of saidcircle and a magnetization direction, wherein one of said magneticelements is so disposed that the magnetization direction thereofcoincides with the axis thereof, and each of said magnetic elementsother than said one magnetic element is so disposed that an angle of themagnetization direction thereof relative to the magnetization directionof said one magnetic element is substantially twice an angle of the axisthereof relative to the axis of said one magnetic element; and magneticcontrolling means for adjusting a strength of the magnetic fieldgenerated by the magnetic field generating means by changing themagnetization direction of at least one of said magnetic elements.